PHYSIOLOGY-employing the term in its more exalted sense, that of the theory of natural phenomena, and restricted in its application to animal beings, according to modern usage,-has made but little progress in the period regarded in this essay. This is not peculiar to the present time: no similar period in any epoch of modern ages presents a much more considerable advancement. Students of this science had long since observed all that an ordinary degree of attention could discern, or that might be arrived at by the usual means of investigation, as well as constituted such theories as might be formed by reasoning powers of the common and general standard. From henceforth it was only new modes of research, or extraordinary powers of intel lect, that could develop any very important original facts, or extend in a considerable degree the correct views of speculative theory. The means of inquiry that has been especially resorted to in modern times, has been that of experiment, prompted in some instances by indica tions originating from the theory of what was already known; in others, undertaken without any preconceptions, or with such only as have been derived from vague and superficial considerations. The recorded results from labours of the former kind are not the most numerous; but those which have been made known are, for the most part, like the discoveries of PRIESTLEY in chemistry,-qualified, by the relations they develop, to increase our knowledge, not merely by their addition, but in a geometrical ratio, where the new terms are the multiplicates of those which precede them. But the fruits of this mode of inquiry are too few, and the difficulty of producing them too great, -as we may learn in regard to chemistry, (which must always be referred to, in preference, when illustrations of the importance of facts and theories, as well as of the different modes of cultivating science, are required,) from the results of the labours of the whole life of such a man as CAVENDISH, devoted as he was to meditation and researches relative to a science where so much yet remained to be known and has since been discovered,-to permit the generality of men, possessing the requisite talents, to pursue it with much assiduity. Hence it is that the history of physiology is so overwhelmed with observations derived from the latter mode of experimentalizing: observations, for the most part, presenting a mere chaos of materials; their narrators not having been able to arrange them, or to draw from them any valid inferences; whilst other men have been deterred from attempting such an object, by seeing, in a considerable proportion of them, nothing but contrarieties; adverse results having been asserted to ensue from the same experiment, when made by different inquirers: whilst, in many instances, from the want of comprehensive views, the servations on the udder of the cow are more curious, and, supposing them correct, remarkably interesting :-he says, he has shown, in some papers written for the Bath Agricultural Society, "that the cow's udder is not a gland, as it is commonly supposed to be, but merely a receptacle for milk, which is chyle, and is formed in the fourth stomach." He says, the fact here stated is "capable of a clear and simple demonstration."-"The cow's ndder," he adds, "is composed of four distinct receptacles, which are commonly named quarters, each of which is supplied by a distinct milk vessel." The elucidation of these points remains to be effected by the papers above alluded to.

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very facts which present the most important links in the chain of causes of those results, have been totally overlooked. But, as this mode of obtaining the title of physiologist requires no great mental exertion, and talents of only the most ordinary kind, the number of its votaries has been so abundant as to enable them to bear down all opposition, to appropriate the field of science almost wholly to them. 'selves, and to induce the greater number of wiser men to retire from amidst the tumult they have raised. Some men, indeed, suppose this to be the only way of acquiring knowledge; and a living French physiologist, who, by chiming in with the popular prejudice, has attained a certain degree of reputation, and made himself the most conspicuous amongst his brethren, is so biassed by his enthusiasm for it, that he would not believe that animals saw with their eyes, unless he had himself proved it by some new experiments on dogs and rabbits. Were it not so common, no absurdity would appear grosser than this of men doubting the correctness of all the observations of others, and expecting that theirs are to be received with unlimited confidence; of men attempting to advance science, and yet being ignorant of the nature and use of human knowledge; of men pretending to regard with consummate contempt all theory, and venting themselves, every instant, the wildest hypotheses. They know not that theory alone is real science; that information of individual phenomena, and the observation of their occurrence, without knowledge of their relations, constitutes only the materials of science, and are useful only when they are properly employed by the theorist. It is with theorists that not only the advancement of the sciences themselves, but also the great practical benefits that have been derived from their application, have originated. Navigators traversed the seas for ages without any other guide than observation of the stars, and, if they are now able to steer to the most remote part of the earth with as much precision as to a port within their view, it is not to themselves, but to geometricians, living in the retirement of their studies, that they can attribute this power. The artizans of Birmingham, with their descendants, would have laboured for ever, as they had done for ages before, without making those improvements of their machinery which they owed to the man whose dwelling-with all its riches, the results of the labours of a long life, comprising the models of machines from which they had themselves derived the most important advantages,-they destroyed with such eager fury, at the end of the last century. Which of the important benefits that have accrued to the useful arts from chemistry, originated with the mere operative chemist, and not with such men as Markgraf, Priestley, Berthollet, Chaptal, Vauquelin, Black, Kirwan, and Davy? It is true that the most important results have ensued from observations of facts apparently the most trivial; but we must not forget that those results have been developed by speculative the orists. The Phoenician sailors, when they saw the sand on the seacoast transferred into a pellucid substance by the ashes of the fire which had served to prepare their food, did not suspect that this substance might enable men to enjoy the best uses of sight long after they must otherwise have relinquished them; that it would permit astrono

mers to penetrate the depths of the heavens and number the stars of the galaxy; that it would display to the naturalist another world, as populous and full of wonders as that which had seemed to offer itself alone to his regards; and that its most immediate application would one day procure for the inhabitants of the coasts of the Baltic, the means of constructing palaces more magnificent than those of Memphis and Tyr, and of cultivating, nearly under the icy atmosphere of the polar circle, several of the most delicious of the fruits of the torrid zone. It was by speculative theorists that all these things were effected; and, as such is the case with other sciences, we cannot, with reason, doubt that it must be so with the more abstruse science of the functions of animal bodies, and the means of influencing those functions so as to remedy their derangements constitutive of disease.

Whilst, then, we regret that such an erroneous mode of cultivating physiology is so prevalent, and that the men best qualified to advance our knowledge, for the most part, deprive the public of the results of their reflections, we must not neglect to pay due attention to the relations of observers and experimentalists, whenever they present facts before unknown, or of which the validity might be doubted. It is such observations, chiefly, that will constitute what is to be here said of physiology, though the present Sketch will not be quite devoid of some reasonings respecting the functions of the spleen of a very interesting character. They originate with Professors TIEDMANN, and GMELIN, of the university of Heidelberg, and are founded on the results of some experiments,* undertaken, principally, with the object of ascertaining whether there existed any other way than that of the thoracic duct by which substances introduced into the intestinal canal might arrive into the general circulation. The results obtained from those researches are not, however, confined to the means of solv. ing this question: they present several interesting facts relative to the digestion, or transformation, of various substances in different parts of the alimentary canal, and the functions of the liver, spleen, and urinary organs. The experiments were made on herbivorous and carnivorous animals, and chiefly on horses and dogs. They consisted in introducing into the alimentary canal various substances which manifest themselves by their colour, odour, and obvious chemical properties; after which the animal was killed, by the division of the spinal marrow between the occiput and the first vertebra, or a blow on the head; and the chyle of the thoracic duct and the absorbents of the intestinal canal, as well as the blood of the mesenteric veins, the splenic vein, the vena porta, and several other vessels, were collected and analyzed. The general results warrant a reply in the affirmative to the question above stated, and showed that chyle alone is absorbed from the intestinal canal by the lacteals; all other substances which pass from the same source into the blood being transported by the mesenteric veins.

The colours of various matters, as indigo, madder, rhubarb, alka

Versuche über die Wege auf welchen Substanzen aus dem Magen und Darmcanale ins Blut gelangen, über die Verrichtung der Milz und die geheimen Harnwege. Von H. TIEDMANN und L. GMELIN, Professeren in Heidelberg. 8vo. 119 seit.

net root, and tincture of turnsole, were manifest, for the most part, throughout the whole intestinal canal; whilst the odours of camphor, musk, and garlic, gradually diminished in the small intestines, and in no instance could be detected beyond the coecum. Alcohol was found in the small intestines. The colours of indigo, madder, rhubarb, alkanet root, and turnsole, were, in different instances, discovered in the urine and in the serum of the blood of the vena porta, but not in the chyle of the thoracic duct or of the absorbents of the intestines. These results are in direct contradiction to those of LISTER, MUSGRAVE, JOHN HUNTER, HALLER, and BLUMENBACH, who all found the colouring matter of indigo in the absorbents of the intestines and in the thoracic duct. The accuracy of the observations of such men cannot well be doubted, and so many positive results in favour of the exist ence of those substances in the chyle are quite sufficient to outvie the negative results of the experimentalists whose observations are here expressly under consideration, even though they happen to be supported by those of Dr. MAGEN DIE. The tincture of turnsole was reddened in the stomach and intestines, in the experiments of Professors Tiedmann and Gmelin. The alimentary mass present in the duodenum also reddens this tincture, but it loses this property as it advances in the small intestines; until it has reached the coecum, where it again reddens the tincture in a very remarkable and especial manner. The fluid secreted by the gizzard and stomach of fowls, and the gastric juice of frogs, also redden the tincture of turnsole. The authors think that the gastric juice contains two different acids, one of which is volatile and the other fixed; the former appearing to be simi lar to acetic acid, the latter lactic acid.

With respect to saline substances, it appears that the earthy and metallic salts are voided to a great extent with the feces. Some of them are absorbed and found in the urine; a very few of them are carried into the thoracic duct, but none of them is present in the blood of the mesenteric veins and vena porta.

Professors Tiedmann and Gmelin infer that the thoracic duct possesses a proper vital contractility, and not merely an elastic force, as stated by BICHAT, MASCAGNI, and several other physiologists; for, on this duct being tied and punctured, in an animal just dead, the chyle springs from it in a jet; whilst this fluid flows from it only in a gentle manner on the performance of the same experiment in an aui. mal some time after death. They witnessed the same results from puncturing the lymphatics in the intestines, loins, and thighs.

The next object of the inquiries of Professors Tiedmann and Gmelin, was the existence of a communication between the absorbents of the intestines and the vena porta. They injected those absorbents, with mercury, in two dogs, a horse, a cow, and three human bodies; and, in every instance, the metal, propelled with the utmost caution, passed into the mesenteric veins and the vena porta. The passage of the mercury from the absorbents to the veins appeared to take place in the mesenteric glands, the veins containing the metal immediately on their escaping from those glands. They think this communication cannot have resulted from rupture of the parts, because a rupture of the veins must have occurred, as well as of the absorbents, in order

that the mercury might enter into the latter, which cannot be consi dered likely to happen from force applied externally to them; and, if the communication depended on laceration of the vessels, it should be expected to happen with the arteries as well as with the veins. Professors Tiedmann and Gmelin think that it is by this route that chyle, as such, has arrived at the vena porta, when it has been found in that vessel; but they do not admit this explanation of the passage of odoriferous and colouring particles, for these were never found in the absorbents of the intestines: they must, therefore, it is inferred, be absorbed by the radicles of the veins; and they think that the liver acts as an organ of assimilation for such substances as are taken up by the intestinal veins. The passage of the whole of the blood of the fetus through the liver before it arrives at the general circulation, may be considered, perhaps, to give some degree of support to this view of the offices of that organ. They have also been led, from the results of the same experiments, to form some original notions respecting the functions of the spleen. They found, in several instances, the absorbents of the whole surface of the spleen filled with a reddish-coloured lymph, which, on being withdrawn from those vessels, soon formed a softish mass, or cake, of a reddish colour, without any separation of serum; a fluid differing in a remarkable degree from the chyle, before it has passed the mesenteric glands especially, as well as from the contents of the other lymphatic vessels. This fact, joined with some considerations on the structure of the spleen, to which they were led by some other observations, have induced them to form the following inferences respecting the nature and functions of this organ.

1°. That the spleen is an organ which has the most intimate con nexions with the absorbent system. 2°. That there is secreted in this organ, from arterial blood, a reddish-coloured coagulable fluid, which is received by lymphatics, and passed into the thoracic duct. 3o. That this fluid, secreted in the spleen and poured into the thoracic duct, serves to assimilate the chyle to the blood. In support of those views, it may be remarked, that the spleen is an organ which is found, in a distinct form, only in vertebrous animals, and these are the only animals which possess a lymphatic system. Lacteals alone are present in any other animals. The size of the spleen, considered proportionally to that of the whole body, has generally a certain relation with the development of the lymphatic organs; so that, in the mammalia, where the lymphatic glands are abundant, this organ is proportionally more voluminous than it is in animals of the three inferior classes, where, as appears from the paucity or total absence of those glands, the absorbent system is much less developed. The great abundance of lymphatics in the spleen has been remarked by RUYSCH, HEWSON, CRUIKSHANKS, MASCAGNI, Sir EVERARD HOME, and many other anatomists. The spleen has a somewhat close analogy in its structure with the lymphatic glands, in its being composed, like those organs, of an intermixture of absorbent and blood-vessels, which have no other excretory ducts than those formed by the absorbents themselves. These analogies had been perceived by Ruysch and Hewson, who also were disposed to draw inferences respecting the functions of this organ