MEDICAL HISTORY
OF THE
EXPEDITION TO THE RIVER NIGER
DURING THE YEARS 1841-2.

CHAPTER II.
HISTORY OF THE FEVER.
Section III.

Causes of the Fever.

No subject in medical philosophy has been investigated with less satisfactory results than the causes of those fevers which, in intertropical countries, are the especial bane of European life. But it can hardly be a matter of surprise to find men of eminence arriving at conclusions of the most opposite and contradictory nature; seeing that endemic fevers are known to prevail during all periods and varieties of season, whether remarkable for protracted rains or unusual drought; and to originate in districts whose situation and geological character are not such as are generally said to belong to miasmatous localities; while, on the other hand, the inhabitants of large tracts of country, of a kind commonly understood to be fertile in the production of fevers, not unfrequently possess an almost total immunity from this form of disease.*

Notwithstanding these perplexing facts, it seems to admit of no doubt that the domain of the worst form of intermittent and remittent fever is to be found, in countries overspread with marshes, abounding in alluvial deposits, with luxuriant vegetation, and subject to periodical inundation, and to a high degree of atmospherical temperature. Such are the Pontine marshes, the maremma of Italy, the too celebrated ditches of Walcheren, and the banks and deltas of some of the great rivers of Africa, Asia, and of some parts of America. Moreover, it is well known that drainage and other means which civilization has suggested have rendered places healthy that were previously notorious for their insalubrity. In support of this assertion, the present comparative exemption from endemic disease enjoyed in our country may be cited. To go further back, Hippocrates states that Abydos, after having been twice nearly depopulated by a pestilential fever, was rendered healthy by draining the city according to his advice. It was one among many of the gigantic schemes of Napoleon to reclaim the Pontine marshes; and authorities, I believe, consider that he would have succeeded had his intended operations been carried into execution. According to M. Thevenot, a late writer on the Diseases of Africa, particularly of Senegal, — from the sanatory regulations and other measures adopted at Saint Louis, with all the disadvantages of climate and soil, — a great progress has been made in public health. In the garrison alone, we have seen that the mortality is lowered from 1-12th to 1-20th since 1829, and from 1-16th to l-20th since 1824.

Supposing, however, it should be generally admitted that soils, with certain conditions of structure and organic products, acted upon by the usual meteoric agencies, generate fevers and other endemic diseases, the inquiry has only advanced a little; for even then, we should possess only a vague knowledge of the means by which this influence is exerted and modified, and still less of the precise nature of the subtle cause thus unaccountably called into action.

Passing over the doctrines of planetary influence, the want of elasticity in the atmosphere, and of animalculae entering the body through various channels, as constituting the poisonous matter of fever — it may be said that the causes have, in the present day, been more commonly referred to heat and moisture, or to both conjoined. A moist atmosphere is supposed to act in various ways: among others, by checking perspiration, and retaining the deleterious exhalations supposed to escape by the skin; by repelling the healthy circulation of the skin, and thus favouring its power of absorption; by withdrawing electricity from the body; and by being a good conductor of miasmata, introducing them into the system through the vessels. Terrestrial exhalations containing the proximate principles resulting from the decomposition of animal and vegetable matter, and the consequent formation of deleterious gases vitiating the air, are considered to be mainly instrumental in the production of endemic disease. Eudiometry has done little to unravel the mystery, as to the constitution of malarious atmospheres. Chemists have endeavoured to unfold the nature of pestilential gaseous emanations, with various and, upon the whole, unsatisfactory results.

Dr. M‘Culloch says, "It has been frequently remarked in Holland, that the severest seasons of fever have followed casual irruptions of the sea, and also that on these occasions there has been produced a degree of putrefaction attended with an insufferable smell, unusual in other cases." Evidence of similar effects from incursions of the sea over embankments, or so as to mix with fresh water, is to be found in various authors. One remarkable case is briefly recorded by Professor Traill of Edinburgh, in his "Outlines of Medical Jurisprudence," and is detailed at greater length by Professor Daniell, of King’s College, London. Dr. Traill observes — "Marshes into which sea water enters are more pestilential than mere fresh water swamps." A striking instance of this is given in the Memoirs of Gaetano Giornini. "A Luccesan engineer, about the middle of the last century, adapted floodgates to the stream in the Littorale of Lucca, which by opening only outwards allowed the land waters to descend, but prevented the sea when driven by the west wind from entering and mingling with the swamps. The Littorale became healthy, and its population increased from 1500 to 9408; marsh fever disappeared except on two occasions since, when by the worming of the gates sea water was insensibly admitted, and on both occasions marsh fever raised its head, until arrested by the repair of this valuable contrivance. The town of Via Reggio, with 2000 inhabitants, stands in what was before an uninhabitable salt marsh, and the mortality in that district, which before the labours of the engineers, even with the system of annual migration during the hot months, was one in fifteen, is now only one in forty, the average mortality in Europe."

In consequence of the unusually rapid destruction of the copper on the bottoms of ships employed blockading the river on the west coast of Africa, the attention of government was called to the subject; and, in 1839, Sir William Burnett, the Inspector-general of Naval Hospitals and Fleets, caused an analysis to be made of several bottles of water taken by me when surgeon of H.M.S. Scout, at various distances off and within the mouth of the river Bonny: the water was found to contain a quantity of sulphuretted hydrogen, besides various proportions of oceanic salts: this analysis was followed by that of several other bottles of water from rivers on the west coast of Africa, by Professor Daniell; and all those from off the river, or near their mouths, contained a notable amount of sulphuretted hydrogen, while those which had been filled a good way up the rivers afforded no trace of this gas. The professor also examined several specimens of copper from the ships’ bottoms that had been injured on the coast, and analysed the black and green crusts with which they were in part covered: the black crust was found to consist of sulphuret of copper, and the green, of sub-chloride of the same metal. Professor Daniell, connecting these results with those derived from the analysis of the waters, concluded that the injury to the copper arose primarily from the sulphuretted hydrogen. In a series of able papers, published in Nos. 2 and 3 of the "Friend of Africa," he explained the formation of this deleterious gas, by the decomposition of the sulphates of sea-water when mixed with fresh water containing vegetable matter: "Decaying vegetable matter abstracts the oxygen from the sulphate of soda, and a sulphuret of sodium is formed: this again acting upon water decomposes it; and sulphuretted hydrogen is one of the products of the decomposition."

From the effects, upon the human body, of air impregnated with sulphuretted hydrogen, Professor Daniell considered that if the water along the whole line of coast, which is intersected by rivers opening into the sea, contained that gas, and were perpetually evolving it, that there was a very probable connexion between such an evolution and the notorious unhealthiness of the coast of Africa.*

In December 1840 Sir William Burnett issued a general memorandum to the medical officers of Her Majesty’s squadron on the west coast of Africa, directing them to examine with great care the waters in the neighbourhood of rivers, with the view of ascertaining the presence of sulphuretted hydrogen, and "to report to him from time to time their proceedings thereupon." A case, containing bottles filled with test solution, was also provided; and Sir William, in his observations and directions for the medical officers of the Niger Expedition, with reference to localities where decaying animal and vegetable matters abound, observes, "although I am quite sure that the inhalation of sulphuretted hydrogen gas is not alone the cause of fever in such countries, yet, as it certainly exercises a deleterious effect upon those exposed to its influence, the steamers should not remain in such situations, and its presence can be readily detected * by the use of the test, with which the surgeon of each ship is furnished." A complete chemical chest fitted up with the necessary apparatus, was most liberally supplied by the government to each of the ships, for the purpose of affording the surgeons every facility to ascertain whether this or any other noxious gas was present in the water, or in the air, on any part of the coast, or within the rivers; and generally of admitting their investigations being pursued to an indefinite extent.

When the ships of the Expedition arrived on the coast, in June 1841, the waters were regularly tested, not only at and within the rivers, but at various distances from them at sea; at Sierra Leone, the river St. Paul, the river Mesurado, the River Sinoe, the Sengana, and the Nun: the experiments were made with great care during all times of tide, and on each occasion one bottle was filled with the water, labelled and hermetically sealed, for transmission to the inspector-general of naval hospitals and fleets, while another bottle was filled, labelled, and corked and sealed with wax in the usual manner: the latter were kept on board for further examination. On the 26th of July, 1841, on opening a bottle, labelled "June 24th, 1841; water, taken eight miles from Sierra Leone;" and another, marked, "July 3d, taken from off the river Mesurado, two miles from the mouth;" both, by their odour, denoted that the water in them was impregnated with sulphuretted hydrogen. In the presence of Dr. Stanger, Dr. Pritchett, and Mr. Roscher, the mineralogist, small quantities of water from each bottle were poured into a series of test-tubes, which afforded a copious black precipitate on the addition of sulphate of copper to one, the same from nitrate of silver to another, and on carbonate of lead being thrown into a third; sulphur was also deposited, on the addition of nitric acid to a small portion of the water. With proofs so unequivocal of the existence of sulphuretted hydrogen, which all of us had failed to detect in water when first collected, an analysis was made of the contents of the respective bottles, with the view of estimating the amount of this gas contained in each of them, and the results were as follows:

In the quantitative estimation of the sulphuretted hydrogen contained in the water from off the Mesurado, the mode adopted was that recommended by Rose of Berlin, which I had before practised, under the direction of Dr. D.B. Reid, namely, by throwing down an insoluble sulphuret, by the addition of a metallic oxide in solution, oxidating by adding nitric acid, and precipitating the sulphuric acid, formed as a sulphate by the nitrate of baryta, and determining the amount of sulphuretted hydrogen therefrom.

The amount of sulphuretted hydrogen in the water taken "off Sierra Leone" was calculated from the quantities of the sulphurets of copper, silver, and lead produced, by adding to it salts of these metals in solution.

Sulphuretted hydrogen was not found in water when first taken up, on any part of the coast, * either previously or subsequently to the above experiments; therefore I feel bound to conclude that the formation of this gas took place after the water was received into the bottles. In both bottles there was a sediment composed of vegetable matter, more especially in the water from off the Mesurado, and there may have been much more of this as well as of animal decomposed substance in an unappreciable state of division. Was it this sedimentary matter acting upon the water in a state of stagnation, or separation from the mass, favoured by a high temperature, that caused the development of sulphuretted hydrogen? or was it the gallic acid, or tannin of the cork, acting upon water containing only a reduced proportion of the oceanic sulphates?

Captain Littlehailes, late in command of H.M.S. Dolphin, informed me, that while lying off themouth of the Nun, in December, 1841, a most disagreeable odour was smelt in the hold of the vessel, which he supposed, at the time, to be owing to brine having escaped from the beef casks, and become putrid below. On minute examination no cause for the smell could be detected, but the hold was cleared, cleansed, and thoroughly ventilated. A case of fever having made its appearance on board, induced Captain L. to shift his berth some miles further seaward. In preparing to weigh for this purpose, it was necessary to get a stage on board, which had been for some days along-side, the people having been employed "hogging" the ship’s bottom. This stage consisted of empty "breakers," (small casks,) lashed together, and on "starting" the bungs a horrible stench issued from them, which was found to be caused by a small leakage of water in each. The winds were very light at this period; the atmosphere was in general in a stagnant state, — the thermometer ranging from 82° to 85°. In fact, the oppression of the weather was such as Captain Littlehailes never experienced before or since, although he had served long in the East and West Indies.

While in charge of the naval hospital at Ascension, in August and September, 1842, it was customary for me to have a large cask filled once a week with salt water, to supply a shower bath, a luxury in which I indulged every morning. On several occasions, it was remarked by Lieut. Foote, (who was living with me at the time,) as well as by myself, that the water in the bath was most offensive, more especially about the end of the week, when the barrel was nearly empty. This induced me to test the water, which was found to contain a very sensible proportion of sulphuretted hydrogen. Ascension, as is generally known, is a volcanic island, about eight miles long and six broad, surrounded by extensive beds of lava and scoriae. Being destitute of vegetation, except on the green mountain which rears its summit among the other numerous old volcanic cones that are dispersed over the island, to the height of 2800 feet, and there being no streams of fresh water running into the sea, the salt water obtained there must be as nearly as possible pure.

It is thus evident that sulphuretted hydrogen may be developed not only in salt water mixed with fresh water containing vegetable substances, but that it may also be produced from pure oceanic water, under certain conditions of temperature, of separation from the mass, and of partial* exclusion from the action of atmospheric air. How then is sulphuretted hydrogen formed under the circumstances in question; and what prevents this gas being generated on the grand scale in the estuaries of the great African rivers, seeing that in those situations the materials requisite for its formation are constantly being brought into contact? There is perhaps no locality in the world whose physical features would seem altogether so favorable to the reaction of organic substances upon the sulphates of seawater, as in the lagoons on each side of the Nun. These are densely studded with the mangrove, contain great quantities of mud, the water in them is always impregnated with sea-water, and in a state of constant stagnation, unless when disturbed by the intrusion of the tides. But the most delicate tests failed to give any evidence of the presence of sulphuretted hydrogen.

I consider the absence of the gas in question from the sea and river waters and superincumbent atmosphere to be distinctly proved: and all that has been observed appears to me to indicate that the production of sulphuretted hydrogen is not the simple consequence of the contact of sulphates and organic matter, but that that kind of decomposition of the organic matter must be first set up which is known as fermentation or putrefaction. This peculiar process is encouraged by matter undergoing the same change, and thus a foul cask might rapidly affect the organic matter of the sea-water contained in it, as in the observation at Ascension. It also requires in general a slight access of air to occasion a preliminary oxidation, which precedes the putrefactive stage; but this access must be slight, for free exposure to air is incompatible with putrefaction, and occasions the destruction of the organic matters by simple continued oxidation, and their conversion into water and carbonic acid.

The putrefaction, then, of the organic vegetable matter is not to be expected in running water or the open sea, when there is the fresh access of air and oxygen.

The matters in putrefactive decomposition are remarkable for their deoxidizing power, taking oxygen from sulphates, and leaving sulphurets, from which sulphuretted hydrogen is evolved by the carbonic acid present. The fermentation of bran is, for this reason, had recourse to, to deoxidize indigo in silk dyeing.

From this view it necessarily follows that no sulphuretted hydrogen was found in the hermetically sealed bottles, because air was excluded and the oxidation, which is a prelude to putrefaction, was prevented. In the corked bottles, on the contrary, a slight permeation of air does occur, sufficient it appears to begin putrefaction, but insufficient to change it into a decomposition by oxidation alone; and finally, in the sea and running streams the vegetable matter appears to be destroyed by simple oxidation, without any putrefaction or consequent formation of sulphuretted hydrogen.

Moreover, the effects of sulphuretted hydrogen would most probably have been shown among the crews at once on entering the river; while we find, on the contrary, that the squadron was healthy until we were at Iddah, twenty-two days afterwards.

The circumstances of the occasional and not uniform production of sulphuretted hydrogen by the reaction of organic matter on the oceanic sulphates, may be said then to remain still an interesting but purely chemical subject of inquiry, to the elucidation of which the observations of the medical officers of the Niger Expedition have, it is hoped, in some degree contributed.

Before taking leave of this subject, I shall add the following remarks of the illustrious Humboldt, relative to the causation of disease in one of the most unhealthy districts in the continent of America.

"When in the bay of Higuerota," says this celebrated traveller, "one of the most unhealthy of the whole coast, where the forests come down to the beach, which is covered with a thicket of mangroves, avicennias, &c. as the shore descends with a gentle slope, the small tides are sufficient alternately to cover and uncover the roots and part of the trunks of the mangroves. It is, no doubt, while the sun heats the humid wood, and causes the fermentation, as it were, of the ground, the remains of dead leaves, and the molluscae enveloped in the drift of floating sea-weed, that those deleterious gases are formed which escape our researches. We saw the sea-water along the whole coast acquire a yellowish brown tint whenever it came in contact with the mangrove trees." Humboldt, struck with this phenomenon, instituted a series of experiments on the infusion of mangrove, the results of which led him to believe, that it was "the moistened bark and wood acting upon the atmosphere, in the forests of mangrove trees, and not the water strongly tinged with yellow, which formed a distinct band along the coast. In pursuing the different stages of the decomposition of the ligneous matter, I observed no appearance of a disengagement of sulphuretted hydrogen, to which many travellers attribute the smell perceived among mangroves. The decomposition of the earthy and alkaline sulphates, and their transition to the state of sulphurets, no doubt, may favour this disengagement, in many littoral and marine plants: for instance, in the fuci; but I am rather inclined to think that the rhizophora, the avicennia, and the conocarpus augment the insalubrity of the air by the animal matter they contain, jointly with tannin. Besides a thick wood covering, marshy grounds would diffuse noxious exhalations in the atmosphere, were it composed of trees which in themselves had no deleterious properties. Where-ever mangroves grow on the sea-shore, the beach is covered with an infinite number of molluscae and insects. These animals love the shade and faint light, and they find themselves sheltered from the shocks of the waves, amidst this scaffolding of thick and intertwining roots, which rises like lattice-work above the surface of the waters."

On entering the river, the squadron was healthy with the exception of a few cases of slight fever, chiefly among the blacks of the Wilberforce, caused by exposure to the rains when watering at Grand Bassa; and one on board the Albert, occurring in a white whose constitution was broken by previous irregularities.

Generally speaking, the crews may be said to have been in a peculiar degree exempt from the more common causes predisposing to disease. The whites were almost all men in the vigour of life, with constitutions fully developed; they were all volunteers, and many of them had already served in warm climates. Their moral condition was good.

The victualling was according to the usual scale of the navy, with this difference, that preserved meats were issued twice a week. Cranberries and pickled vegetables were also served out on salt-meat days. The water of the river was found to be perfectly purified and wholesome by adding a little lime to it. A cup of coffee was provided for each white man before going on deck in the morning, and quinine dissolved in wine was frequently administered in ten-grain doses to all hands. Flannel dresses were always worn in the evening, and also during the day when the atmosphere was moist. Fires were also kept burning in the various compartments as occasion required. The awnings were constantly spread, and when it rained they were sloped. The greatest attention was paid to the dryness of the clothes, and the proper airing of the bedding. The oil-cloth covering the decks was kept cleaned. Hair-cloth, being a bad conductor of heat, was hung over the ship’s sides to defend the iron from the sun’s rays. The only Europeans exposed on the deck during the night were one officer, a quarter-master, and the sergeant or corporal of marines.

A reference to the Meteorological Tables will show that the atmosphere was in general far from being moist; the dryness of the air indeed increased as we advanced upwards, and it was remarkable at Egga, so that it can hardly be supposed that the body was predisposed to disease, by the atmosphere carrying off its electricity by induction, or by impeded exhalation from the skin. I regret to say, that I cannot produce, as I intended, a series of experiments on the electric condition of the atmosphere, while in the river, and will not therefore even venture upon a hypothesis as to how far it was concerned in the causation of the disease.

On the other hand, it will be seen in the brief detail of the progress of the vessels through the Delta to Iddah, the Confluence, and afterwards to Egga, that we had traversed (and slowly) a country of a character recognized as eminently fertile in the production of fever. Swamps in a rich alluvial soil abounded. The islands and banks were everywhere more or less inundated. The vegetation was rank and profuse. The ships’ companies were necessarily a good deal exposed on deck during the day, and were sometimes harassed by frequent anchoring and weighing in ascending the river. The actual labour cannot be said to have been great, but there was a degree of restless anxiety inseparable from being constantly liable to be called on deck. The upper deck was much lumbered, in a degree preventing the free circulation of the air. The same cause no doubt stood in the way of the decks being thoroughly cleansed.* Notwithstanding that the room on the lower deck was proportionally greater than that of ships in the navy generally, yet so many men sleeping below under so high a temperature must have tended to dimmish the vital energies, and consequently to lower the resisting powers to disease. The thermometer on the lower deck was seldom under 84° Fahr. The precaution of defending the ships’ sides has been mentioned, and no doubt it was so far beneficial. The fires were "banked up" at night, in order to weigh and get up the steam next morning at daylight. Thus there was an unavoidable source of heat, which was constantly being diffused throughout the vessel by the active conductivity of the material of which she was composed. It will naturally be said that the vessel’s construction of iron was favorable to her acquiring the temperature of the medium in which she floated, but it is at the same time to be borne in mind that the water of the river was seldom under 83° Fahr.†

When it is considered, as has been already noticed, that the vessels were constantly exposed to endemic influence, while they remained in the Niger, it is impossible to say at what time the miasmatous poison was first inhaled; but I hardly think that it was imbibed by any individual before we left the mouth of the river: if this were so, then fever maybe said to have ensued on the sixteenth day* from the period of its earliest imbibition. Quarter-masters, seamen, and marines, whose duties were chiefly on deck, stokers in the engine-room, cooks, and in short, men of various occupations and constitutionally dissimilar were simultaneously affected with fever.

Upon the whole, I am inclined to think that in those cases which appeared at Iddah, the germs of the disease were contracted in the Delta. The stagnant state of the atmosphere, (relieved by occasional tornadoes,) and the causes of malaric exhalation being still abundant, and accumulated in the lower part of the atmosphere, from the want of a wholesome agitation, were favorable to its development at Iddah. Up to this point, the south-west breeze had always been felt during part of the twenty-four hours. The miasma in this state of condensation, so to speak, acted energetically upon men whose vital powers were already enfeebled, and who may have been for some time insensibly under its insidious influence.

Moral causes came also into operation after leaving Iddah: many of those who were well were dispirited, and not a few, when taken ill, became speedily despondent.

When out of the whole expedition there were only fifteen whites that were not attacked with fever in the Niger, it is scarcely possible to offer any opinion as to how far the susceptibility to this treacherous disease was influenced by temperament or idiosyncracy. Of the blacks, consisting of natives of various parts of Africa, including Kroomen, Americans, West Indians of African origin and East Indians, to the number of 158, eleven only were affected by the fever in the river: they (the eleven) had all been in England, and for some years absent from their respective countries. The disease in them assumed a comparatively mild form, and in no case did it prove fatal; showing that the immunity from endemic disease in warm countries, which is enjoyed by the dark races, is to a certain extent destroyed by a temporary residence in another climate.

The question as to whether contagion contributed to the spread of the disease on board of the ships may, in my opinion, be briefly disposed of. All were exposed to the same influences, and nearly all were attacked with fever. Two only of the four medical officers who died had been in attendance on fever patients. Dr. Pritchett, Mr. Thomson, Mr. Stirling and Dr. Stanger were among the few who escaped being seized with fever, although they were in constant intercourse with the sick; and I was the last person in the Albert laid down with fever. The nurses on board the Albert were among the latest taken ill, and one escaped altogether. No fact came under my observation affording the slightest evidence that the disease was communicable from one person to another.

Does one attack of river fever afford any protection against a second?

My own experience, added to information obtained from many of my brother officers, and from Mr. King, the surgeon of the Ethiope, who has been more in the Niger than any other medical man, is wholly unfavorable to the opinion that one attack of river fever affords any immunity from a second. On the contrary, those who have once suffered from this treacherous disease seem particularly predisposed to it, if they again venture within malarious influence. Of those who had the Niger remittent, on hoard the Wilberforce in 1841, many were again attacked with fever, on the return of the vessel to the coast the following year, while surveying the Cameroon river and Amboises islands; and when that vessel proceeded up the Niger the second time, in July 1842, six out of seven who had already passed through river fever, were again seized with it, from the effects of which two died. In many cases the character of the second attack may not be exactly like that of the first, but Mr. Stirling, who saw the patients on the return of the vessel to Fernando Po, considered the fever as in no way differing from that which had come under his observation when in the river during the previous year.

But it seems after all to be a matter of no great consequence to establish a precise identity of character between primary and secondary attacks, if the agencies originating remittent and intermittent are admitted to be the same; the production of the one form or other depending upon intensity of cause or peculiar susceptibility or idiosyncrasy of constitution. Whether the second attack be developed in the form of a remittent or intermittent, sufficient evidence is afforded that the system possesses no immunity in virtue of the first attack, for both diseases are essentially the same, differing only in degree.

I have thought it right to record the results of my experience with regard to this important feature in the remittent fever of African rivers, on account of its practical bearing with reference to the selection of men for service on the west coast of Africa, more especially those who are likely to be employed in rivers. Indeed the whole history of the fevers of warm climates is unfavorable to the opinion, that in any one of them is any absolute protection against a second attack secured by a first.

Arejula the Spanish physician, Sir W. Pym, and Sir James Fellowes were the most strenuous advocates of the doctrine of protection, which has been confuted by Drs. Bancroft and Ferguson, and particularly by Sir W. Burnett,* who disproved many of the statements made by Sir W. Pym relative to the yellow fever of Gibraltar, upon which his opinion was based.

A further investigation of this subject was instituted by the Anglo-French Commission during the epidemic at Gibraltar, in 1828, of which M. Louis was president, the late Sir David Barry, vice-president, and M. Trousseau, secretary.

M. Louis assumes nine thousand as the smallest number of patients exposed to two epidemics, seen by the medical men examined by the commission; and states that they had to deliberate on only thirteen cases of presumed second attacks, of whom a majority of the commission declared one case of double attack evident, three probable, and the others doubtful or inadmissible.

It has been a matter of question, how far the period at which the vessels entered the river was well chosen. To solve this question in any degree satisfactorily, it will be necessary to appeal to the generally recognized physical causes of fevers in swampy districts, and to those practical facts which have come under the observations of non-professional as well as professional men who have been much in Africa.

Experience has abundantly taught that the rivers of Africa are at all periods more or less unhealthy; and if it be admitted that the effluvia causing fevers result from the decomposition of organic matter, (animal and vegetable,) or from exhalations from soils recently under water, then the season at which the river is high must be, theoretically, the least prejudicial to health.

It is on the immediate banks of rivers that the greatest accumulation of animal and vegetable detritus is found; and, as the river rises, the banks at length are many feet below the surface, and in a condition not likely to evolve gases into the atmosphere above. It is true that the river, during the extension of its limits, is daily bringing those organic bodies with which it comes in contact to a condition favorable to decay. The elements for pestilential effluvia are present, but they remain inert so long as they are covered by the waters.

As the rains cease, and the river falls, the case is completely altered. From day to day a greater surface of muddy soil becomes exposed, and the organic matters, saturated with water, are now powerfully acted upon by the sun, and gaseous emanations are abundantly evolved.

Divesting the subject of theory altogether, what do practical men say on the subject? Captain Midgely, a most intelligent man, who has been upwards of twelve years a regular trader to the Bonny, speaking of the season of 1841, says, "This season the rains ended unusually abruptly with the month of September, and sickness immediately ensued. There was little or no sickness in Bonny until the 1st October, since which it has been more than usually unhealthy, even for the season, for eight out of ten of the vessels have lost from two to five men each; and when I left Bonny, four days since, every vessel in the river had men lying in a very doubtful state." At Aboh, Iddah, the Confluence, and at Egga, the people declared that "bad bellies," fevers, eruptive and other diseases, proved very fatal during the dry season.

It is not to be understood that I imagine the causes that have been under consideration, the sole agents in bringing on fevers; but the action of the sun upon moist soils furnished with organic matter certainly contributes to their production, and this is, in a great degree if not altogether, prevented when the river is high.

My object is only to show that the time at which the expedition ascended the river, if not more healthy, is at least as healthy as any other period of the year, with this advantage, that a full river enables a more rapid transit to be made through the Delta than is possible when the water is low.

Latency of the Poison. In no case did the fever break out before the sixteenth day after commencing the ascent of the river, or sooner than the twenty-first day from entering the river. The Albert, Amelia, and Soudan were twenty-three days inside the river before fever made its appearance, and the Wilberforce about two days less; therefore, as the invasion of the disease was nearly, if not wholly, simultaneous on board the ships, a case may be said to have occurred in the Wilberforce on the twenty-first day.

Assuming that the poison was not inhaled until the vessels steamed upwards, which will reduce the period of latency to the shortest probable duration, and taking the cases on board the Albert, the ship the longest in the river, I find that out of fifty-five cases among the whites, and six among the people of colour entered in England, the days of seizure were as follows: on the 16th day, three; on the 17th, two; on the 18th, two; on the 19th, three; on the 20th, four; on the 25th, one; on the 26th, three; on the 29th, three; on the 30th, three; on the 31st, three; on the 33d, five; on the 34th, four; on the 35th, two; on the 36th, one; on the 37th, six; on the 42d, three; on the 45th, one; on the 47th, one; on the 48th, one; on the 51st, one; on the 60th, three: average day of invasion 33.286. Among the six people of colour, two were attacked on the 16th day, one on the 18th, one on the 21st, one on the 29th, and one on the 42d day; making the average period of attack the 25th day, (25.200.)

Bearing also in mind that about one ninth of the white crew escaped the river fever altogether; that the people of colour only who had resided for some time in a temperate climate were affected by it, but in small proportion and in a mild degree; and that the blacks entered in Africa did not suffer at all, — we shall have some data for the selection of crews for future operations in the Niger.

During the period when the river is high, a steam vessel, combining light draught of water with good speed, carrying three white officers, including a surgeon, coloured engineers, and manned wholly by Kroomen and other natives of western Africa, might enter the Niger, and avoiding unnecessary delay, reach Aboh, Iddah, the Confluence, Egga, and Rabba, and return to the sea in less than fourteen days.*

The places just mentioned constitute a field whereon to base operations that may afterwards be carried out to an indefinite amount by properly cultivated native agency, and the employment of the least possible number of white people.

The comparatively civilized state of the inhabitants of Rabba, its position, the enterprising character of its ruler, and the present extension of Fulatah influence throughout the Niger, are valid reasons for opening up intercourse with this city. The importance of this measure has already been pointed out by Captain Trotter, and will no doubt be still more urged by him.

With regard to the special medical means for preventing attacks of the fever, nothing certain can be stated; I would, however, recommend the daily use of quinine, with a good diet, and a moderate allowance of wine; in short, that the body should be an exhaling rather than an absorbing surface: I would also advise the liberal diffusion of chlorine, protection from the sun, and other precautions elsewhere detailed in this work.

Supposing, in spite of all care, that one or the whole three whites imbibed the germs of the disease while in the river, but that it was not developed until after they had gained the open sea, there is every reason to believe that its character would be considerably modified, and the danger proportionably diminished.

TABLE OF EXPERIMENTS TO DETECT SULPHURETTED HYDROGEN.

(These data are not included here)