They are found growing in and upon both vegetables and animals. Nees von Esenbeck imagined, that minute forms multiplied themselves in the atmosphere; and really, when we consider the amount of effluvia composed of the atoms cast off from the bodies of living or decaying organic matters, which are incessantly pa.s.sing into the atmosphere, the conjecture is not an unreasonable one. The minuteness of those, which we know are always found growing on decomposing bodies, does not preclude the possibility, nay, further favours {121} the probability, that others infinitely more minute,[48] may be destined to remove the more subtle and vaporous particles which escape into the air.

We can, therefore, I think, conclude, that the lower tribes of vegetation, may consistently be regarded as capable of existing in almost any condition, and almost under any circ.u.mstances, they may be made to grow in plants by inoculation, as shewn by De Candolle, and Dr. Ha.s.sall. If the stem of wheat also is inoculated with vibriones, they will make their appearance in the grain.[49] If the seed contain them and have not lost its germinating properties, these worms will be found again in the grain. If the grain containing them be dried for years, and moistened again with water, these animalcules, according to Bauer and Steinbach, will present all the phenomena of life. This experiment I have witnessed, and can confirm the statement. These animalcules in the diseased grain, have under the microscope the appearance of an immense {122} number of eels crowded together in a small s.p.a.ce, and presenting a movement more, perhaps, vermicular than any other, and it is continued for a considerable time. Now if these animalcules, or their ova, can be proved to pa.s.s with the sap to the seed, there can be no difficulty in comprehending how germs, considerably more minute and of a vegetable nature, should be found subject to the same peculiar mode of obtaining an entrance into animals and vegetables for sustenance. "It is usually imagined," says Dr. Carpenter, "that the germs liberated by one plant are taken up by the roots of others, and being carried along the current of the sap, are deposited and developed, where vegetation is most active."

The chemical theory of disease would be better sustained by a comparison of "the artificial formation of alkaloids," and the phenomena of transformation of blood into the tissues of animals, and their degeneration into effete matters, and of sap into the tissues of plants and their degenerations.

Professor Kopp of Strasburg, says, "In a chemical point of view, the alkaloids are remarkable for their composition, for their special properties, both physical and chemical, and for the interesting reactions to which many of them give rise, when exposed to the influence of different reagents. Considered medically, the organic bases are distinguished by their energetic properties. They {123} const.i.tute at the same time, the most violent and sudden poisons, and the most valuable and heroic remedies."

Upon this very intricate and interesting part of chemical philosophy, it is rather dangerous to enter without a thorough and practical knowledge of the subject. This, however, falls to the lot of few men. We, who are engaged in the study of disease, and of the best methods of cure, are obliged to take the investigations of the a.n.a.lytical chemist, and examine them for ourselves in the intervals of leisure allowed us during the active exercise of our calling. Though with less advantages for the study of these transcendental relations of organic and inorganic matter, we are not, nevertheless, precluded from forming our opinions on their practical bearings to the phenomena and treatment of disease.

That there is a matter of a poisonous nature concerned in the production of endemic and epidemic affections, cannot be doubted by any one; I believe indeed, that the chemical theorists admit this, at all events Liebig does, for he says, "The morbid poison changes in the blood are fermentative, just such as occur in beer making." If we start, then, with the consideration that poisons, in a chemical point of view, are the objects of our research; the obvious course to take is to enquire what is the source of poisons generally, and what their effects on the animal economy? The mineral poisons are entirely excluded from the enquiry by their {124} inapt.i.tude for diffusion, and their uniform effects upon all persons, differing only in degree in their operation. The same objections apply to gaseous poisons, except that to them the property of diffusion would be admitted.[50] We come then to the alkaloids, which const.i.tute, as Kopp says, the most violent and sudden poisons. For the production of alkaloids by artificial means, organic products of some kind are required. Artificial heat, powerful chemical agents or length of time, are, as far as information at present extends, the indispensable requirements to induce these peculiar changes in matter. The only instance I can find, in which elementary matters can by artificial means be combined, so as to resemble the products of nature, is that of the conversion of carbon and nitrogen into cyanogen.

But the process by which this is accomplished, leads rather to doubt whether it be really and simply by a combination of _elementary_ carbon and nitrogen. I extract the following from the Annual Report of the Progress of Chemistry, for 1848. "H. Delbruck has performed some experiments on the important subject of the formation of cyanogen. He confirms the statements of Desfosses and Fownes, inasmuch as a _weak but distinct_ formation of cyanogen was observed on igniting {125} _sugar-charcoal_[51] with carbonate of pota.s.sa in an atmosphere of nitrogen." The use of sugar-charcoal, may be perhaps an explanation of the weak formation of cyanogen, for in these numerous and successive chemical changes of matter, it is impossible to say how many sources of error may arise. The constant contradictions of each other, and the opposite statements made by chemists, of equal eminence, leave us in a wilderness of doubt, from which we are not likely to be freed, until definite laws shall be discovered to act as a guide in the comprehension of the higher branches of Chemical Philosophy.

But supposing that the generation of alkaloids could take place in the body, or some a.n.a.logous poisonous matter, we have yet to imagine a whole host of peculiar and essential conditions to effect this change, besides an atmospheric agent or agents to set in motion those compositions and decompositions, capable of bringing out these new products from the elements of blood. We are aware that in the blood, carbon and nitrogen are sufficiently abundant as well as saline compounds, to generate cyanides, and, with hydrogen also there in plenty, hydrocyanates, and thus from them many other poisonous products, but how is all this to be effected? And even if effected, it is yet a question if such compounds can in any way simulate the attacks of epidemic disease. We have {126} already shewn that the amount of most poisons necessary to destroy an individual, can be pretty clearly estimated, and their _modus operandi_ is tolerably well understood.

Again, the most essential part, in which all chemical theory fails, is an explanation of the reproduction of contagious matter.

The catalytic process, by which decompositions are said to be effected, and in which Liebig includes the various fermentations, is one of those chemical relations of matter to matter, considered by some as the probable cause of infection. Mr. Simon, in a late lecture, has said, "I consider the phenomena of infective diseases, to be essentially chemical, and I look to chemistry to enlighten the darkness of their pathology. Qualitative modifications, affecting the molecules of matter as to their modes of action and reaction, are such as form the subject of chemical science; and those humoral changes which arise as the result of infection clearly fall within the terms of its definitions." Further on he adds: "The phenomena of infected diseases appears then, in many respects, to be sui generis.

Certainly they are chemical. _Probably_ they belong to that _cla.s.s_ of chemical actions called _catalytic_."[52]

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It is not improbable that something resembling a catalytic action may take place in the blood in those diseases of endemic and epidemic origin, but that it can be by a chemical process alone is contrary to all experience of catalytic operations, for except in the instance of fermentation proper, there is no multiplication of the fermentative matter. The action of the matter of contagion seems to stand on the confines between electro-chemical and bio-chemical manifestations, and so long as no chemical explanation can be given for the multiplication of the matter of infection, the most rational course to adopt is to a.s.sume that life under some unknown form is, as we every where find it, the sole reproductive agent.

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SECTION II.

THE ANIMALCULAR THEORY OF EPIDEMICS UNTENABLE.

The animalcular theory of disease, after remaining almost unnoticed for nearly two centuries, has been again revived under the auspices of Dr.

Holland in this country, and Henle of Berlin. And though not entirely buried in obscurity, this theory had completely failed to modify the practice of physicians in the treatment of those diseases which were supposed to owe their existence to these invisible atoms of created being.

The resuscitated notions and all their amplifications, to which the advance of science has contributed so much, are threatened with a like fate, an absence of all practical results.

Though I would not attempt to deny the possibility, nay, even the probability, that insect life may yet be discovered as the cause of some diseases,[53] still {129} there are many and cogent reasons against both, and which are at variance with facts and observations. Where insect life has been found a.s.sociated with disease, it more especially appears as a consequence than as a cause.

Disease, in its most enlarged sense, is a conversion of one form of matter into another; it is a transformation of healthy blood and tissue into new and abnormal products. Where insects in all their variety of forms are discovered, their voracious propensities are their chief characteristics, they are the consumers of matter after its partial disintegration, if animal matter be their food, unless they be carnivorous and predacious, or if herbivorous they usually feed upon the tender shoots of plants. Thus far we are certain of the manner in which insects destroy living matter; it is a process the una.s.sisted eye may every where witness, and which experience has amply attested. To take, however, the animalcular world as it presents itself to us under the microscope, and as the intermediate step between the manifest and the hidden for a fairer and more direct method of reaching the truth, what do we observe to be the ruling law of infusory instinct? They live to feed; the term polygastrica sufficiently implies their natural tendency to consume. The simplest form of animalcular life, seen in the genera of monads, still preserves the animal character by possessing a stomach or stomachs in which the food is received, to be digested for the nourishment of the {130} system; and even some of these minute objects which vary in size from one _two-thousandth_, to one _three-thousandth_ of a line in diameter, are said to be carnivorous and predacious. Upon this fact alone, I would place the improbability of insects being the cause of epidemic disease. Each insect doubtless has its own peculiar food, and whether it be a vegetable or animal feeder, it consumes the matter already organized for conversion into its own tissue, and the only change which could be affected by them in the blood, would necessarily be that of appropriation of some one of the const.i.tuents as an element of food; when that food is digested, (taking digestion generally as an identical process,) the excrement.i.tious matter is composed of secretions and disorganized matter, mixed together as an _effete_ product, and destined then for reorganization by the vegetable kingdom. Now all animals, whether they be large or small, live on organized matter,--they convert that matter into an inorganic form, and I cannot help imagining that if epidemic diseases and fevers depended upon animalcular growth and development in the blood or tissues of the body, the excretions or secretions from them would have yielded some information to the searching enquiries of the chemist, supposing that these excretions and secretions were capable of reaching to a sufficient amount in quant.i.ty, to bring about those fatal effects of poisoning, we witness in Cholera and other epidemic affections. Insects, I {131} believe are poisonous only by their secretions, and though they are known to multiply with exceeding rapidity, I can hardly imagine that by their development, however rapid, they could produce such a change in the human body, as to bring about the speedy dissolution, and generally gangrenous appearance, that has invariably been observed in those suddenly dying under the influence of epidemic poisons. The vibriones, whose destructive effects on wheat are so well known, are a genus of animalcules, which at first would seem to favour the animalcular theory in a remarkable manner; for on examining them, they do not appear to possess any other structure than a gelatinous absorbing ma.s.s, in this respect resembling a vegetable.

But Ehrenberg's scrutiny corrected the error of De Blanville, and shewed, that they were far from being agastria, or stomachless animals. The Rev.

William Kirby says, "Ehrenberg has studied the vibriones in almost every climate, and has discovered, by keeping them in coloured waters, that they are not the simple animals that Lamarck and others supposed, and that almost all have a mouth and digestive organs, and that numbers of them have many stomachs." All the discoveries indeed which have been made on the minuter forms of animal life, have tended to confirm the doctrine that the stomach is the exponent organ of an animal; that is, in all animals there exists, in a variety of modified conditions, a receptacle for food. Some of the {132} animalcules, however, are still supposed to exist by absorption, as the vinegar eel, _vibrio anguilla_,[54] but when we find that the law is, generally speaking, that the receptacles of food become multiplied in number in these minute beings, and the vibriones which were supposed to be stomachless, have been proved to emulate their a.s.sociates in the number of these organs; it would be more reasonable to conclude that our imperfect vision is the barrier to their detection, rather than to suppose that they do not exist. Besides, when we are told on undoubted authority that some of the animals of this cla.s.s, have as many as _forty or fifty_ stomachs; the least we can do, is to allow that all of them possess, at least one digestive organ, though we may not be able to detect it.[55]

So far then for the consideration of animalcular structure: let us now more particularly enquire into their destructive habits, and their functions, inasmuch {133} as they may be supposed capable of engendering epidemic diseases and fever. The truly carnivorous animalcules, or those truly herbivorous in their instincts, we may presume to be beyond the limits of our enquiry. We have rather to do with those which take an intermediate position, namely, those which feed upon matter undergoing decomposition, or upon fluids containing organic matters in solution, or suspension. If we take Entozoa generally, they may be considered as most conveniently to be placed in this intermediate cla.s.s; and here we find still the digestive apparatus, and more than this,--for upon the modifications of the organs appropriated to digestion is their cla.s.sification founded. "Rudolphi divided the Entozoa into Sterelmintha, or those in which the nutrient tubes without a.n.a.l outlet are simply excavated in the general parenchyma, and into the Coelelmintha, in which an intestinal ca.n.a.l with proper parietes floats in a distinct abdominal cavity, and has a separate outlet for the excrements."[56]

How do these animals obtain their sustenance, and what changes can they produce upon the vital fluid of the body? a.n.a.logy is here our only guide.

If the trichina spiralis is examined, it is found to be enclosed in a cyst containing fluid; and this is, {134} doubtless, the source of its nutriment, and contains in solution the elements for its nutrition; but in this instance there is no selection, and there can be no locomotion to an extent sufficient to imply searching for food, as the animalcule in its natural state, when taken from the human muscle, is found coiled upon itself, making about two and a half turns. The fluid of the cyst is thus in all likelihood prepared by endosmosis, for the immediate and appropriate nutrition of the parasite. The cyst is thus the part which performs the diseased process, the containing animalcule is merely the consumer of what is prepared for it by the cyst. And this would seem to be the rule with all parasites, of the encysted kind.

We have alluded to the vibriones which are found in the fluids of living bodies, and the trichina which is found in the solid muscle; we have now to refer to those which infest the cavities. It was, I believe, Ehrenberg, who shewed that the tartar which acc.u.mulates on the teeth is composed of the debris of minute animalcules; in fact, that it consists of calcareous matter, having once formed a portion of the structure of their bodies, the ubiquity of these creatures is therefore as much and clearly established as the lower forms of vegetation. The intestinal worms, of which perhaps the Taenia is the most curious and important to be noticed, are from the locality in which they are found, chiefly injurious by the irritation they set up, and by appropriating {135} to themselves the nutrient juices elaborated in the process of animal digestion, thus depriving the individuals they infest of that which was destined for their own nourishment. In this, as in all a.s.sociated instances, the character by which these parasitic animals are marked is their consuming propensity.

There is, however, one more observation to make upon parasitic growths; but the question is yet unsettled in what kingdom of nature is the acephalocyst, or hydatid, to be placed. Mr. Owen says, "As the best observers agree in stating, that the acephalocyst is impa.s.sive under the application of stimuli of any kind, and manifests no contractile power, either partial or general, save such as results from elasticity, in short, neither feels nor moves, it cannot, as the animal kingdom is at present characterized, be referred to that division of organic nature."

We thus arrive at the simple cell, and the multiplication of living beings by cell buds; it is the point at which the confines of the animal kingdom are reached, and at which we are driven to speculation. The hydatid lives like a plant, by imbibition; and procreates, like a plant, by budding, either endogenously or exogenously, as regards the original or parent cell.[57]

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This condition of being, suggested the notion of Protozoa, or first animals, in the same way that the purely cellular plants, that is, each individual, consisting of a single cell, gave the idea of Protophyta, or first plants. Mr. Kirby thus expresses himself on this subject: "The first plants, and the first animals, are scarcely more than animated molecules, and appear a.n.a.logues of each other; and those above them in each kingdom represent jointed fibrils."

Admitting, then, that animals as well as plants exist in the form of simple cells, and that their multiplication proceeds apparently upon the same principle in each, it is nevertheless abundantly manifest, that the cellular form of perfect individuals is infinitely more numerous in the vegetable than in the animal kingdom.

{137}

From the mosses downwards to the fungi, the whole structure of the plants consists of an aggregation of cells, more or less in number and complicate arrangement, until, through a variety of gradations, we reach the single cell as a perfect individual.

It is rather remarkable, that the lower forms of vegetables and animals seem to derive their nutriment from matter of a similar kind; and though the office of plants is as a rule, to convert inorganic into organized matter, it appears that some of the fungi may live as animals do on organic matter when in a state of solution. This, however, is uncertain; for we do not know what are the first signs of decomposition in organized bodies, and for aught we can tell, it may be perpetually going on; so far as the disengagement of carbon from the system is concerned, this is certain; but whether the nitrogenous compounds also are subject to a resolution into their elements in the living body, is another question, and not so easy of solution. The partially decomposed elements of animal structures are, however, particularly adapted for the nutrition of the lower forms of vegetation; it is, indeed, from the decaying organic matters that the fungi derive, it may be said, their entire food.

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SECTION III.

SKETCH OF THE PHYSIOLOGY AND PATHOLOGY OF PLANTS AND ANIMALS.

Animals and plants depend for their existence upon a nutritive fluid, which permeates their structure; it is the element from which all their secretions are formed, and their organs are nourished.

The food of animals is composed of previously organized matters, and is conveyed into a reservoir called a stomach, where it undergoes a process of solution, previously to entering the circulation. At this period, the animal and the plant again present points of resemblance, the lymphatics or absorbent vessels take up the products of digestion, and convey them to the blood-vessels, where mingling with the current of the blood, they are conveyed to the lungs, there to undergo a process of oxygenation before they become fitted for the renovation of the tissues of the body. Such is the nature of the food of man, that it contains all the elements necessary and adapted for transformation into bone, muscle, brain, and parenchyma, as well as the other tissues of the body; besides other elementary matters, which, though they form a very insignificant portion of {139} animal textures, from their constant presence in the vital fluid, evidently perform some important offices in the general economy of life; they are partly, perhaps, occupied in forming const.i.tuents of secretions.

Plants do not require a stomach,--the humus or soil to which they are fixed is the laboratory, where the nutritive matter is prepared in a state fit for absorption by the spongioles of their roots, and these correspond to the lymphatics of animals; after being taken up by the spongioles, this new fluid mingles with the sap, and pa.s.ses to the leaves or breathing apparatus of plants, where carbonic acid gas combines with the crude vital liquid, and converts it into a condition fit for all the offices to be performed by the plant: viz. the growth of tissues, and the elaboration of secretions.

The tissues, however, of plants, though more simple in their nature, present a much more varied character than those of animals, when the different species are compared.

The bones of animals which give them their form, are invariably const.i.tuted of phosphate and carbonate of lime, deposited in a matrix of gluten; muscle, nerve, brain, tendons, and ligaments, have nearly, if not completely, an identical composition throughout the whole range of the animal kingdom: their secretions, however, vary much more considerably, as also do the secretions of vegetables. But vegetable tissue may contain, as in the stems of {140} gra.s.ses, a considerable amount of silex, and some notable quant.i.ty of sulphur, and so essential to their existence is the former element, that they cannot live without its presence in the soil, and also with it an alkali, to render it soluble. A large amount of soda, is an invariable attendant upon the structure of marine plants, as potash is of those growing on the land.

Thus, whether we regard the health of animals, or vegetables, we discover, that besides the matters which are absolutely indispensable for the nutriment of the tissues which undergo rapid transformation, those of a more permanent and durable nature require in an almost insensible degree, a rest.i.tution of elements; and though not apparently absolutely necessary to preserve vitality in the being, yet have so marked an influence over it, as to indicate an extensive bearing of each individual part, on the whole a.s.sociated ent.i.ty.

The elementary tissues of both kingdoms have been traced, in whatever form they may be found, to a cellular origin. The minutest vegetable germ, is a cell containing a granular matter within it, and even man himself, in his embryonic state, may be represented as an insignificant point in the realms of s.p.a.ce; and might be placed side by side with the smallest particle of living matter, without suffering by the comparison.

The laws by which the development of these elementary cells is regulated, so that each advances {141} to its limit, and fulfils its destination, is one of those inscrutable and overwhelming mysteries of nature, which leads the admirer of creation on and on into the abyss of the future, and fills his soul with aspirations for that time, when the veil of ignorance shall be withdrawn. But this is not my subject.

The organization of the two animated kingdoms, is then regulated by definite laws, and all matter, whether acting upon them as agents of nutrition or destruction, are equally under their dominion; to investigate and to endeavour to fathom some of these laws, is the aim I have in view.

The sap is to the plant, what the blood is to the animal,--the elements of nutrition and secretion are contained in it, and whatever interferes with its normal const.i.tution by subtracting from, or adding to it, deteriorates its qualities, and r.e.t.a.r.ds or accelerates the functions of the individual.

Excess or deficiency of the natural elements may also be a source of disturbance; if carbonic acid be too abundantly liberated in the soil, as Dr. Lindley expresses it, "plants become gorged;" and if, on the other hand, the elimination be too slow, they become starved. It has been also shewn, that plants though they give out oxygen from their leaves, do not throw it off as animals do carbonic acid from their lungs; but that this arises as a result of digestion, and the fixation of carbon in the system, and that they really respire oxygen as {142} animals do, and give off carbonic acid, both by day and night.

That light is the stimulant of the digestive functions, and that, therefore, during the day, the amount of oxygen thrown off, far exceeds the amount of carbonic acid liberated during the same period.

The great and important distinction between animals and plants is, that the former possess a nervous system, by which they are subject to a very extended series of psychological relations; it is in these chiefly, if not entirely, that we are to look for the distinctive and well-marked differences of diseased action. In animals there are special media of communication between the sources of dynamic power, and the parts upon which the force is exercised: and again, a return communication exists, which conveys impressions to the source of power, and to use a simple comparison, a system of telegraphing is in incessant and watchful operation. This force is influenced and modified in its action, when exercised in the regulation of nutrition, growth, and reproduction of tissues, by the pa.s.sions and emotions of the mind. All the secretions and functions of the body are more or less susceptible of being accelerated, r.e.t.a.r.ded or modified by the psychical relations of mind and matter. Though we are apt to imagine that in man alone, these phenomena obtain much importance--there can be but little doubt, that wherever a {143} nervous system exists, whether in the form of aggregated or diffused ganglia, the interdependence of force and organization, each upon the other, bears a certain and definite physiological comparison; the more aggregated the ganglia, the more close, intimate, and extensive the psychical connexions, and the gradations pa.s.s downwards, until they appear to be lost on the confines of the vegetable kingdom.

The diseases of plants and animals deserve a more careful comparison than, I think, has. .h.i.therto been bestowed upon them.[58] If the study of physiology, or an enquiry into the laws which regulate the functions of living beings in a state of health, has been materially aided by the intimate knowledge of vegetable physiology, which, from the simple structure of plants, so favours the experiments of the student, there is every reason to suppose that vegetable pathology may also lead us to an equally important and useful result.