Imatges de pÓgina

till, in the course of ordinary causes, they are developed and brought to maturity, that the controversy between the involutionists and the disseminists has been maintained ; and were it not that no opinion is too absurd for a lover of theory to hold and to teach, we could hardly have believed that men calling themselres philosophers would ever have indulged in such conjectures as the following. “In maintaining this invisible pre-existence, some have imagined that the namerous generations of each species were, as soon as created, packed up together, either side by side, or one within the other, like concentric strata in a bulbous root, in a parcel so small as not to be visible, and then so deposited in the frame of their first parents, as to be successively and gradually evolved by the future processes of generation. This is the theory of involution."-" The less ingenious and the more inexpert who could not comprehend this intricate mode of packing and unpacking, which was puzzling even to Bonnet himself, have generally preferred the mode of disseminating them all at once, scattering them abroad as soon as created, through the regions of space, to people the air, the waters, and the earth, and there to wait for proper opportunities of insinuating themselves into those natural parts, that may be unoccupied, and neither too old nor too diseased for developing their contents. This is the theory of dissemination."

Dr. Barclay, who seems to like a joke, makes himself very merry at the expence of both these classes of theorists. The involutionists are pressed with many puzzling queries, in regard to the nature of their packages and the mode of their transference from one subject to another. It is, no doubt, a scriptural expression that the whole human race were in the loins of their first parent Adam, but it is obviously a form of speech grounded on a figure, and not meant to be taken literally as a strict physiological statement. Leibnitz, bowever, and several of his followers, dismiss the metaphor and seize the apparent fact. Ainsi je croirois," says that ingenious writer, que les ames, qui seront un jour ames humaines, comme celles des autres especes, ont été dans les semences, et dans les ancêtres jusqu'a Adam, et ont existé, par consequent, depuis le commencement des choses, toujours dans une maniere de corps organisé, en quoi il semble que Monsieur Swammerdam, le R. P. Mallebranche, M. Bayle, M. Pitcairn, M. Hartsocker, et quantité d'autres personnes trèshabiles soient de mon sentiment. Et cette doctrine est assez confirmée par les observations microscopiques de M. LeeuWephook, et d'autres bons observateurs."

As to the disseminists, on the other hand, they are not treated with either more reserve or greater respect. They. are asked, how their germs, wandering in empty space in search of babitations, are able to distinguish their own species ; how they obtain information of the particular parts which are suited to their purpose, and ready to receive them; how, after this information is obtained, they discover the way by which they are to enter; whether by the breath, along with the food, or by the absorbents opening on the surface; -whether after the select few are developed, which the usual wants of the species require, or after the appropriate parts are incapable of developing more, myriads that remain in their primary state immediately retire in search of other receptacles, or remain till the spirit of the body in which they reside be summoned to a tenement beyond the grave: and these are questions which no author has yet been able to answer.

Bonnet, the celebrated naturalist, was, as we have already. hinted, an involutionist, but with the characteristic modesty of his gentle nature, he seems unwilling to hazard the strife of controversy, even for the sake of a favourite hypothesis. " Je n'ai pas decidé entre l'hypothese de l'emboitement et celle de la dessemination des germes : J'ai seulement donné entendre que j'inclinois vers l'emboitement." Generation, of course, according to the theory of this latter scbool, was only a process of developement, or expansion of the germs transmitted from age to age in the persons of a thousand ancestors, and finding at length a combination of circumstances suited to their naturalization. This view of the subject, however, is surrounded with numerous difficulties, which Bonnet was ready to acknowledge, and even prepared himself to explain. In his work on organized bodies, he labours to unfold some of the mysteries connected with the developement of germs, particularly how, during their expansion, they are occasionally turned into monsters ; and how by the intercourse of two individuals of different sexes and species, they are sometimes converted into mules or hybrids; and finally, how, after continuing to exist without any change in an infinite variety of circumstances for thousands of years, they may at last in this temporary passage through the bodies of two individuals, contract the diseases, habits, dispositions, structure, and form, by which these individuals are characterized.

Haller was originally a decided anti-involutionist, being of opinion that the structure of the offspring is formed by some generative processes in the bodies of the parents. At length, however, yielding to what he imagined the force of truth, he

took his place among those whom he had formerly opposed, and espoused the notion of pre-existing germs. The conversion of such a man was a great triumph to Bonnet and Spallanzani, who regarded the change of opinion effected in the mind of tbat distinguished physiologist, together with the supposed facts which gave occasion to it, as the strongest of all evidence in support of their hypotheses. But the progress of discovery which had secured for them this splendid victory, threatened by its further advancement to weaken the foundations of their power, and even to overthrow it altogether. “ Aniinalcula Infusoria,” observes our author, " were found to spring suddenly in both animal and vegetable infusions, or according to Fray, in mineral mixtures, not through a regular and continued series of generations, but without parents, as if by a new and original creation. Spallanzani and Bonnet, who not only remarked, but also contributed to establish the fact, had bere to renounce their favourite hypothesis of involution, to adopt that of dissemination, and to admit that the process of developement by generation was not universal. Still, however, they adhered to the hypothesis that plants and animals had all been existing since the creation, and tbat these animalcules, though utterly invisible, had from time immemorial been existing in the air, the water, or the earth, waiting opportunities for their own peculiar modes of developement; but as none was supposed to have had its residence in the element of fire, that element was employed as a test to ascertain in which of the three remaining elements they principally resided. For this purpose the animal and vegetable matters of the infusions were boiled, roasted, subjected even to the heat of tbe blow-pipe, and immediately shut up, not only in vessels accurately corked, but hermetically sealed. Animalcules notwithstanding sprang up in numbers, when the vessels were capacious. It was then supposed that the germs might bave been existing in the water which had been inclosed along with the animal and vegetable matters: upon this the water was previously distilled, and afterwards examined minutely through the microscope before it was enclosed ; an examination evidently superfluous, as by the hypothesis germs are not visible until they are partly at least evolved. The suspicion next fell upon the air, and more particularly as a smaller number, and in less variety, appeared in vessels of narrower dimensions where the air was scanty, and they never made their appearance at all when the infusions were confined in vacuo. But the air was also exposed to boiling heat, after it was inclosed. From whence then came the animalcules?”

Amidst these experiments and hypotheses, each physiologist preferred that particular interpretation of facts which best accorded with bis previous habits of thinking. Spallanzani embraced that view of them which gave countenance to his favourite notion of the pre-existence of germs; imagining that the temperatures to which, in the course of his experiments, he bad exposed the animal and vegetable matters employed by bim, must have destroyed the vegetative powers of any particles of which they were composed ; not reflecting, as Dr. Barclay well observes, that the like temperature would have also destroyed the vegetative powers of any of his germs. Needham, on the contrary, who was engaged in similar experiments, and was personally acquainted with Spallanzani, was rather inclined to ascribe the origin of these animalcules to certain properties in the particles of matter, but without pretending that these properties were either essential or underived, as obviously appears to have been the opinion of his friend Buffon.

Since we have mentioned Needham in connexion with Buffon, we cannot refrain from reminding the reader how far, in the case of these authors, the paltry spirit of personal ambition tarnished the love of science and the purity of friendship. Engaged in the same pursuits, and guided by the same views, they prosecuted their experiments together, and appear for a time to have communicated freely to each other the new lights which they succeeded in throwing upon their favourite study. Buffon, however, in relating these experiments in the second volume of his Natural History, creates in the mind of his reader the impression that they were chiefly his own. He mentions Needham, indeed, but it is only incidentally and as a subordinate person-a species of treatment which provoked the indignation of the Jesuit, and induced bim to publish in his own defence.

Buffon, as well as his coadjutor Needham, denied the preexistence of germs, and yet with singular inconsistency maintained the existence of certain embryos, which in favourable circumstances were capable of combining so as to become, entire plants and animals. Plants and animals are therefore to be viewed as consisting of a multitude of germs—a fact of which proofs may be drawn, says he, even from the more common and inferior species, such as worms, polypi, elms, willows, and many other plants and insects, every part of which contains a whole, and in order to become a plant or an insect, requires only to be unfolded or expanded. Considering organized bodies in this point of view, an individual is a whole uniformly constructed in all parts, a collection of an infinite

number of particles every way similar, an assemblage of germs, or minute individuals of the same species, which, in certain circumstances, are capable of being expanded, and of becoming new beings, like those from which they were originally separated.

Buffon, however, was neither steady nor consistent in his views. Reflecting upon the numerous experiments made by himself, by Daubenton, and Needham, he began to suspect that their conclusions had exceeded the warranty of their facts-that the moving particles which they had seen in the seminal fluids, and in a variety of both animal and vegetable infusions, were not decidedly embryos or germs. These particles, no doubt, were most abundant in the semina of animals and the seeds of plants, but they were also found in a variety of substances which had been exposed to a roasting heat; and what farther convinced him that they were not animals, was that they moved only for a time in a certain direction ; moved without intervals ; and when once stationary, moved not again, and never were observed to propagate their species. From these circumstances, as well as from the absence of certain other characters, esteemed necessary to the constitution of germs, Buffon concluded that he saw in the moving atoms or animalcules, a kind of living and organic particles, equally adapted to the formation of every species of organized structures, whether plants or animals; all of them too being, as he thought, precisely of the same species ; not the result of any process of generation; not the effect of any animal or vegetable process; but substances constituting the aniversal semen-the causes, not the consequence of organizationnot germs, but the primary incorruptible elements of all germs, and ultimately of all organized substances.

Dr. Barclay is very successful in exposing the absurdity of Buffon's system, particularly as it respects the moulds in which the organic particles are supposed to assume the several forms of the animals and vegetables whose species they are employed to perpetuate; and also in regard to the functions of these particles in the process of generation. We must not indulge in the details of this part of the physiological bypothesis. Suffice it to say, that Buffon revives the epicurean notion that the seminal fluid is an extract from all the different parts of the body: and imagines, of course, that the organic particles proceeding from the head will arrange themselves in the bead of the foetus, those from the feet will go to the feet, those from the right side of the parent to the right side of the child, and those from the left to the left. " But,” says our author,

« AnteriorContinua »