In this respect there is a marked difference between an epidemic and an endemic affection; for when an epidemic disease attacks a city or town we do not discover that the central parts are more exempt than others; indeed, it is rather the contrary; for the most crowded parts of towns and cities are those, if not exactly in the centre, which would be comprised in a s.p.a.ce nearer to the centre than the circ.u.mference; and it has been in those parts generally where the epidemic influences seem to have exercised the most potent sway. One would more naturally suppose, that a city surrounded by {99} paludal miasm, and not itself being capable of generating the poison, should be more affected at the circ.u.mference, from the simple fact that the paludal germs, which rise in the air, are suspended in the fogs and dews of the atmosphere. These, unless widely dispersed by the winds, would remain within a comparatively confined s.p.a.ce; and those situations nearest to them would be most subject to their influence. Besides, it has been shewn, that a small wood or hill, or even a wall, has been sufficient to cut off or obstruct the paludal miasm.

Without enumerating all the known endemic diseases, two or three may be alluded to for our present purpose; viz. that of shewing that endemic and epidemic diseases have a similar origin.[39]

It is well known that under certain favouring conditions an endemic may become a malignant and pestilential disease; that Yellow Fever, which is always endemic in the west, Cholera in the east, and the Plague in the south of Europe and north of Africa, every few years takes on an epidemic form, and desolates considerable tracts of country.[39]

The Pestilence which raged in the summer and autumn of 1804 in Spain, commenced at Malaga, and remained for a considerable time confined to its {100} boundaries, in consequence of the measures of precaution that were used, in preventing all communication between the inhabitants of the infected city and those living in the surrounding country. It was only in consequence of persons escaping through the cordon, and pa.s.sing into the interior of the country, that the disease spread, and extended its ravages to distant places.

It appears to be quite clear, that this disease may properly be considered in the first instance of endemic origin; but the tendencies, atmospheric and otherwise, were such as to favour its multiplication in other districts than that in which it first came into active existence. From this we may infer, that the seeds of the disease were dormant, and only became roused into vital activity by fortuitous circ.u.mstances. Dr. Rush states, that the endemic disorders of Pennsylvania were converted, by clearing the soil, to bilious and malignant remittents, and to destructive epidemics. Dr. Copland says, it has been observed, especially in warm climates, and in hot seasons in temperate countries, that when the air has been long undisturbed by high winds and thunder-storms, and at the same time hot and moist, endemic diseases have a.s.sumed a very severe and even epidemic character.

Dr. Robertson also confirms this view. "Endemic diseases, in cases of neglect and preposterous management, are found to become more malignant even in the most temperate climates; and to {101} generate a matter in their course, capable of producing a particular disease in any circ.u.mstances. _Indeed the origin of every_ contagious fever unattended with eruptions, with the exception of Plague, must commence in this way."

Why Dr. Robertson should except eruptive Fevers and Plague I cannot understand, for they must have had a commencement; and their many points of similarity indicate, if not an identical, an a.n.a.logous source to other endemic fevers.

It will doubtless be generally acknowledged that endemic and epidemic diseases depend upon some unknown agents, having their source in malarious districts, and being capable of a.s.suming either a contagious or non-contagious character, according to circ.u.mstances.

If, therefore, we find that under any conditions an endemic affection becomes capable of being propagated by contagion, the same law will hold with regard to it as to the Plague; that the power of reproduction in this matter is evidence of life, according to the doctrine laid down in the earlier part of this work. But whether or not infection be admitted, a matter generated in a malarious district, if confined in its effects to that district alone, would not necessarily imply an inorganic nature of the poison; for it is difficult to understand how inorganic poison, prevailing generally over a certain tract of country, could select particular individuals for its victims. If chloroform, chlorine, carbonic acid, sulphuretted hydrogen, or even spores of poisonous fungi, (as {102} supposed by Mitch.e.l.l, which, as he regards their effects, would act in a similar manner to inorganic compounds) were the agents, all persons would suffer more or less, and the majority be similarly affected. We do not find that uniformity of symptoms, which attend upon the exhibition of poisons in the ordinary acceptation of the term, poisoning. This subject shall be more particularly considered, when treating of the influence of organic germs on animals and plants.

The history of the Eclair steamer is particularly interesting, as shewing the extraordinary tenacity with which the germs of disease attach themselves to vessels, which we may call floating houses.

The crew of the Eclair contracted Yellow Fever on the coast of Africa, and a number of them died. The remainder, sick and well, landed at Bona Vista, one of the Cape de Verde Islands, and the vessel underwent a process of washing, whitewashing, and fumigating. Nevertheless, on the return of the ship's company, the disease broke out again with equal intensity, and the vessel was ordered home. Sixty-five out of 146 officers and men, who composed the crew, died of the disease before reaching Portsmouth, and twenty-three were sick at the time of arrival.

Eight days after the Eclair left Bona Vista, a Portuguese soldier who had mixed with her crew died in the fort which had been occupied by them. Other soldiers then fell sick, and the fort was abandoned. The fever still spread.

From the 20th September, when the first soldier {103} was attacked, to the first week in December, the fever continued to rage, and at that period it had found its way into almost all the country villages. The fever was believed to be the genuine black vomit fever; it proved contagious almost without exception to the nurses of the sick.

This is an abstract of Mr. Rendell's letter to Lord Aberdeen, Mr. Rendell being British Consul at Bona Vista.

Now at the time the fever broke out in the island the weather was extraordinarily hot, and much rain had fallen, and the town itself was badly drained and in a filthy state; can it be imagined then that the seeds of a disease liable to a.s.sume a pestilential character should lie dormant or be annihilated under circ.u.mstances the most favourable for their development, especially when we know that endemic diseases may a.s.sume a malignant character?

This is just one of many cases which confirm our opinion in this respect, that plants and diseases are not long in making their appearance where the soil and atmosphere are congenial.

The tenacity with which the disease attached itself to the Eclair is sufficiently explained in the absence of due ventilation; in fact, that in the first instance there was no ventilation at all in the hold of the ship.

This also the more readily affords a clue to the disaster through all its stages, first in the contraction of the disease as an endemical affection in the vessel; secondly, in the multiplication of the {104} germs in the damp ill-ventilated hold, in a warm climate; and thirdly, the persistence and entire localization of the disease to the vessel when it arrived in the climate of the British sh.o.r.es; while, fourth and lastly, in the unusually hot and damp island of Bona Vista, the seeds of the disease were sown, and, as we might expect, multiplied indefinitely.

The consecutive attacks of the crew of the Eclair shew that here a noxious gas or a vaporized inorganic poison could not have been the cause of the disease, for as I have before said, in this case the attacks should have been simultaneous; we find, on the contrary, that as the depressing effects of the melancholy condition of the crew was almost hourly undermining the health of the stoutest of them they as surely became the victims. The Kroomen, or natives on board the ship had not suffered, shewing that they were inured to the miasm, or were dest.i.tute of that condition of blood which would be favourable to a propagation of the materies of the disease.

The Eclair we learn had left Bona Vista eight days when the first victim breathed his last; this would give perhaps three or four days for the incubation of the disease in the patient, or supposing he had not contracted the germs of the disease before the crew of the Eclair left the fort, some local favouring conditions were the means of keeping the germs in a fertilizing state, for it is clear from this spot the infection spread as from a centre or focus. {105} Such instances as these might be multiplied to extend the length of the enquiry, but, I think, to little advantage. The chief facts to be gathered are that an endemic affection became epidemic and pestilential, contrary to its usual mode, for the Portuguese official physician, on being consulted by the Governor of the Island as to the safety of landing the contaminated crew, said, "No danger at all; I have often brought sick men on sh.o.r.e coming in vessels from the African coast, and I never knew any ill effects to arise." Putting the most reasonable construction on this emphatic and straightforward language, we may presume that ordinary, remittent, and yellow fever had been commonly imported into the island, for it is not to be supposed but that both forms of disease must have existed among those sick men who had "_often been landed_," under the sanction of the Portuguese physician.

To take another instance; intermittent fever or ague, is a disease known among almost all nations of the world, but it usually occurs in the endemic form only. It is universally supposed to depend entirely upon marsh effluvia, and we are accustomed to consider it as attaching only to low lying countries;[40] but this is not always the case, for disease in {106} this respect, like vegetation, may be found in various lat.i.tudes, to accommodate itself at varying alt.i.tudes, to the temperature and climatic relations, so as to appear indigenous. But though our prejudices are in favour of a simple miasmatic source of ague, as its sole cause, there are some who believe in its infectious nature. M. Sigaud, in his work on the Climate and Diseases of Brazil, speaks of Epidemics of _grave intermittent Fever_, and Dr. Copland says, that the epidemic prevalence of ague is a better established fact than its infection, and has been admitted by most writers.[41] We have, therefore, but to go one step further to arrive at infection, after having found that an endemic disease under peculiar circ.u.mstances, though but rarely, becomes {107} epidemic. The number of persons attacked by ague in a malarious district, in proportion to the population, is not so great as might be expected, considering that they are always subject by night and day, more or less, to respire the air containing the germs of intermittent fever; we might, therefore, deny the paludal source of the affection, as reasonably as deny infection, if we found that occasionally, persons, though subject to all the usual influences, yet escaped all injurious consequences.

There are grades and varieties of infectious diseases, from the most inveterate to the most mild and doubtful; but that all, without exception, which can in any way be traced to a specific generating and organic cause, may a.s.sume an exalted infectious character, and that the most inveterate, on the contrary, may more resemble the mild and doubtfully infectious forms, is a conviction that must be forced on all who pursue this enquiry with unbia.s.sed interest.

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CHAPTER III.

THE REASONABLENESS OF THE APPLICATION OF THE FACTS TO THE INFERENCE.

SECTION I.

THE CHEMICAL THEORY OF EPIDEMICS UNTENABLE.

It has been inferred that the germs of disease possess the property of vitality, and a number of facts have been adduced to support the proposition that vitality is the indwelling force by which the matter generating epidemic and endemic disease exercises its influence over man and animals. The reasonableness of the application of these facts to the end in view has now to be considered. Chemistry cannot account for epidemics.

Our first subject of reflection points to the chemical discoveries of the last few years, and particularly to those of the great German chemist Liebig. We find in the first paragraph of his Organic Chemistry applied to Physiology and Pathology, the following words: "In the animal ovum, as well as in the seed of the plant, we recognize a certain remarkable force, _the source of growth_ or increase in the ma.s.s, _and of reproduction_ or of supply of the matter consumed; a force in a state of rest. By the action of external influences, by impregnation, by the presence of air and moisture, the condition {109} of static equilibrium is disturbed. This force is called the _vital force_, _vis vitae_, or vitality."

The doctrine of Liebig, that the vital force manifests itself in two conditions, or rather, that it is known to be in two different states, that of static equilibrium as in the seed, and in a dynamic state, as in that of growth and reproduction, is perfectly applicable to the germs of disease; the static equilibrium is referrible to the matter of vaccine lymph when dried and preserved for use, and the dynamic forces of the matter are known to be in operation during its reproduction and growth in the system of the vaccinated child.

Then as to reproduction of matter by any chemical process, our author can furnish us with no examples, for even in his explanation of the causes of disease he is quite silent on this point, merely acknowledging that diseased products must be either rendered "harmless, destroyed, or expelled from the body." He further says, that "in all diseases where the formation of contagious matter and of exanthemata is accompanied by fever, two diseased conditions simultaneously exist, and two processes are simultaneously completed," and that it is by means of the blood as a carrier of oxygen that neutralization or equilibrium is established. Liebig thus admits that an agent exists in the blood, capable of deteriorating it at the expense of the oxygen, which he maintains is contained in the red globules; he further acknowledges that two processes of diseased {110} action are going on at the same time, and though he does not explain them, I imagine him to mean that new contagious matter is generated and eliminated from the blood, and that at the same time, there is that condition of body which he would call simply a diseased state, and characterizes it thus: "Disease occurs when the sum of vital force which tends to neutralize all causes of disturbance, (in other words, when the resistance offered by the vital force) is weaker than the acting cause of the disturbance."

If I rightly apprehend his notions, they perfectly harmonize with my ideas, to a certain extent, on the subject. They accord, at any rate, most completely with the theory attempted to be established, and fully confirm the reasonableness of the application of the facts recorded to the inference drawn from other sources. The difference only rests on the question whether vitalized or non-vitalized matter is the _fons et origo mali_.

How is the production of new matter, resembling that originally causing the disease, to be explained by any known hypothesis, except on the a.s.sumption of living organized matter? Though Liebig and Mulder both deny the fact, that the Torula cerevisiae is the sole agent in the process of fermentation: they both equally fail in shewing upon what it does depend, and their difficulty rests entirely on their incapacity to explain the uniform reproductive properties of the matter engaged in this, as well as in all other allied operations. Liebig's statement {111} however on this matter requires notice--he says, "that _putrifying_ blood, white of egg, flesh and cheese, produce the same effects in a solution of sugar, as yeast or ferment. The explanation is simply this; that ferment or yeast is nothing but vegetable fibrine, alb.u.men or caseine, in a state of decomposition."

This state of decomposition, however, involves a much more complex proceeding, than simply a reduction of matter into its elementary forms of gases, earths, and minerals; for we nowhere find decomposition of this kind going on without the development of some organized bodies, either animal or vegetable: and since we have seen that the spores of the cryptogami are always in existence in the atmosphere, and making their appearance under favouring conditions, and especially when we find that fermentation is invariably accompanied, and I may safely say, preceded by the deposition in the fluid of the sporules of the Torula, we can hardly believe that they are any other than the sole agents of the process. I have now a considerable quant.i.ty of the Torula obtained from the urine of a diabetic patient, in which they appeared, as it were, spontaneously. After the urine had been allowed access to the air for a certain time, and the whole of the saccharine matter was converted into new compounds, reproduction of the Torula ceased;--and those which remained when the process was completed, still continue as organic cells, deposited {112} in the bottle in an inert state, but ready, on the addition of fresh sugar, as has been proved, to resume an active existence. These germs, it is now well known, may be dried into powder, so as to be blown away like dust without any, or but little, detriment to their vital energies; and there is now no doubt that they exist in this condition in the air, as do the spores of mucor, aspergillus, oidium, agaricus, and all other fungi.

Mulder, however, does allow some properties to the yeast vesicle; he says, "a variety of strange ideas have been entertained respecting the nature of yeast; recent experiments have convinced me that it undoubtedly is a cellular plant consisting of isolated cells. They resemble the composition of cellulose in some respects, but differ from it in many." "These vesicles, consisting of a substance resembling that of cells, do not contribute in the least to the fermentation, but are exosmotically penetrated during fermentation by the protein compound." These chemists seem to have an instinctive horror of allowing any active properties to the yeast vesicle, that is as far as the conversion of sugar into carbonic acid and alcohol is concerned in the act of fermentation. Dr. Carpenter, as if desiring to conciliate the chemical and physiological disputants, considers that the truth is to be found in the mean of the two extremes,--that is, that the process of fermentation is neither entirely dependent on chemical laws, nor on those laws which preside {113} over the growth of reproductive matter, but is a process in which both perform certain offices, each depending on the other to produce the combined result; he thus approaches more nearly to the theory of Mulder, than that of Liebig.

But to revert to Mulder, he speaks of the Torula cells being "exosmotically penetrated during the process of fermentation by the protein compound." Now the Torula is acknowledged to be one of the Fungals, and the chemical const.i.tuents of the Fungi approach very nearly that of animal tissues. They contain a peculiar principle, residing in and obtainable from them, termed Fungin, which is as highly azotised as animal fibre. The protein compound alluded to, Mulder says, is not gluten, because insoluble in boiling alcohol, and not alb.u.men, because it is very readily dissolved in acetic acid, and he regards it as a superoxide of protein. This superoxide of protein can only have been produced by a vital action in the cells of the Torula, and as the fungi consume oxygen, and give out carbonic acid, we clearly have all the elementary conditions for their growth in almost all decomposing animal and vegetable matters. It is the nature of the fungi to live on organized matter, but always when it has a tendency to decay; it is for this reason they have been called "Scavengers." Again, we can understand why some animalized or nitrogenous matter should be necessary for fermentation, otherwise fungi could not grow, nitrogen being an essential const.i.tuent of {114} their structure, and further fermentation does not commence without the presence of oxygen, and like as in animals, this gas supports their existence. The conversion of sugar into alcohol is represented by the following formula:--

RESULT.

Sugar. Alcohol. Carbonic Acid.

Hydrogen 3 3 Oxygen 3 1 2 Carbon 3 2 1

If therefore the process were merely of a chemical nature, where is the necessity for atmospheric oxygen to accomplish the end? it is quite certain that fermentation cannot go on without its presence. Let us compare the action of ferment or yeast in a dried state to the action of alb.u.men, which Liebig says is sufficient when decomposing to set up fermentation. "The white of eggs when added to saccharine liquors requires a period of three weeks, with a temperature of 96 F. before it will excite fermentation."[42] But any saccharine liquor on exposure to the air, though entirely dest.i.tute of alb.u.men or gluten, will ferment, and the Torula may be found in it. I have found the Torula in a great variety of syrups which have spontaneously undergone fermentation. I have also discovered that the development of the cells is delayed or accelerated by the nature of the ingredient used in flavouring {115} the syrups, with other peculiarities which need not here be mentioned.

But the conversion of starch into sugar by means of gluten requires some notice, as by some persons it is a.s.sociated in their minds with the organic process of fermentation.[43] Mulder ascribes the latter in the first instance to the action of heat, evidently believing that the pseudo-catalytic operation of gluten upon starch is the type of all such actions, and regarding them all as simply chemical, but we here distinguish a wide difference; in the latter instance the gluten is decomposed, and rendered unfit for a repet.i.tion of the chemical phenomenon, and if it is desired to renew the action fresh gluten must be obtained, and a certain temperature kept up, otherwise the experiment fails. How different is fermentation: in the ordinary temperature of the atmosphere the yeast vesicle will multiply, no incremental or unnatural addition of heat is requisite, and it is one of the commonest and most natural instances of vegeto-chemistry: the grape cannot shed its juice, nor the sugar cane its sap without admitting these germs, which, under certain {116} conditions multiply themselves and convert the saccharine elements into new compounds.

The method by which the conversion of starch into sugar is accomplished is thus described by Dr. Ure. He says that if starch one part be boiled with twelve parts of water and left to itself, water merely being stirred in it as it evaporates, at the end of a month or two in summer weather it is changed into sugar and gum, bearing certain proportions to the amount of starch used. But "if we boil two parts of potato starch into a paste, with twenty parts of water, mix this paste with one part of the gluten of wheat flour, and set the mixture for eight hours in a temperature of from 122 to 167 F. the mixture soon loses its pasty character, and becomes by degrees limpid, transparent, and sweet, pa.s.sing at the same time first into gum and then into sugar."--"The residue has lost the faculty of acting upon fresh portions of starch."

Four points of contrast present themselves for notice as elements of comparison with true fermentation. 1st. The starch solution has to be boiled, so that heat, by which it is to be supposed that the starch globule is ruptured, seems to be an essential portion of the chemical change, and even this may in fact alone be sufficient in such a case to produce some elementary change in the starch, and may prepare it for the subsequent catalytic action of some related organic, though not vital material.[44]

{117} 2nd. Not only a summer heat is necessary, but a period of one or two months time must elapse before the starch with the water simply becomes converted into sugar, and if artificial heat is to be used to hasten the operation, a temperature from 122 to 167 F. must be resorted to in order to obtain the desired result. 3rd. When even this is accomplished there is no reproduction of the fermenting matter, and artificial and chemical means must again be applied to repeat the experiment. 4th. The conversion of starch into sugar can be accomplished without the presence of gluten at all, by the aid only of temperature and time. It seems to me, therefore, to be entirely unnecessary to occupy more s.p.a.ce in the elaboration of a proof of the doctrine that the germs of the Torula are the sole agents in the conversion of saccharine fluids into alcohol and carbonic acid. By another chemical process starch can be converted into sugar, but I am not aware that hitherto any method has been discovered by which sugar can be converted into alcohol except by the process of fermentation proper.

I have been thus particular in commenting on this subject, as it bears, in an especial manner, on the question under consideration.

{118}

The physiologist cannot afford to lose this process from the category of chemico-vital, or biochemical manifestations.[45] The philosophy of the age has a tendency to make every thing chemical; it is true that the Divinity is as much seen in the laws which govern the elementary particles of matter, as in those laws which preside over the trans.m.u.tation and sustentation of those elementary and inorganic particles, when compounded in the tissues which are engaged in the formation of living beings. The laws by which acids and alkalies neutralize each other, and the affinities single, double and elective, which the particles of matter exhibit, together with the influences of light, heat, and electricity upon almost every condition of matter, are as truly wonderful as the creative power.

Man may, in many instances, imitate the processes of nature, he can render iron magnetic, and form alkaloids, but the {119} laws which govern the particles of matter are still the secret of the whole proceedings. We do but interpret the language of nature in discovery, the book is ever open before us, and every atom of the world is a word and a theme, capable of occupying the short span of sublunary existence allotted to man. We have read of "sermons in stones," but a book has been written on a "pebble."[46]

To return, as we every where in nature find a gradual transition in the forms, arrangements and properties of matter, so we may expect to find a link between the inorganic and vital chemistry of nature. The fungi, by which we contend this transition appears to be accomplished, are also a link in chemical composition, between the animal and vegetable kingdom, and not only in that, but in their subsisting upon matter which has been organized, they are deoxidizers and reducers, as the vegetable kingdom in its highest function is a compounder. To their functions and offices in the great scheme of creation, we may fairly apply ourselves with a sure and certain result of the most interesting discovery. Is it no hint that wherever decaying organic matter is found, there do we find fungi? is it no hint that they are found in all parts of the world? that even in snow the germs of fungi will grow and multiply to such an extent, according to Capt.

Ross, that the protococcus was seen {120} by him, clothing the sides of the mountains at Baffin's Bay, rising, according to his report, to the height of several _hundred feet_, and extending to the distance of _eight miles_?

Even stones contain in their interior, or inters.p.a.ces of their structure, the germs of fungi. A species of Tufa is found in the vicinity of Naples of a porous texture, which, when moistened and shaded, produces vast mushrooms, four or five inches high, and eight or ten inches broad.[47]

This author further says: "In the Maremma, where the volcanic tufa is the basis of the soil the surface is intermixed with the animal remains of departed empires, and the ordure of cattle, is covered with gra.s.ses of old pasturages, and is wet with heavy dews. Everything, therefore, conspires there to a fungiferous end."