pancreas, it is a sort of abdominal salivary gland, and it appears certain that when it is diseased, fatty matter is often ejected from the bowels, its office being, probably, to render that substance miscible, and fit to be taken into the circulating fluids.

But reserving this and other matters relating to the chemistry of digestion for the present, we merely observe that the chyme produced by the action of the gastric juice on the food, and afterwards changed into chyle, is absorbed from the villi of the intestines, in part by the veins going to the liver (the peculiarity of the vena porta being known to Beranger), and also by the lacteals. These last were described by Aselli, in 1621, the lymphatics afterwards by Rudbeck and Bartholinus, and the thoracic duct by Pecquet, in 1649, previously known, however, according to Portal, to Eustachius. Mascagni and our Cruikshank have been the great delineators of this system, whilst the structure of the glands situated upon these vessels, and supposed to be the elaborators of their fluid, was investigated by the wonderful skill of Ruysch and Malpighi.

The chyle and fluid from the lymphatics, the latter probably little different from the former, and nutrient in its quality, together with the venous blood, enter the heart by the two great ascending and descending veins; that portion of the blood which ascends from the digestive organs, having, as alluded to above, previously passed through the liver; the descending column having also received the contents of the thoracic duct, derived from the lacteals and lymphatics. The blood enters first the right reservoir of supply, the auricle, it is then forced into the right ventricle, unlike the auricle, exceedingly strong and muscular, and consequently by it the blood is expelled into the lungs by the pulmonary aorta. Between the auricle and ventricle, and between the ventricle and aorta are two sets of valves of different construction, and so beautifully adapted to prevent regurgitation as always to have excited the admiration of the anatomist, and to have led many to understand the course of the

C

blood through the heart before Harvey's time. In the lungs the blood is submitted to the action of the oxygen of the air which we breathe, absorbing it, and being decarbonised by giving out a nearly equal volume of carbonic acid gas, thence also becoming vermillion-coloured instead of modenared. This operation must be accomplished through the pulmonary membrane by a species of endosmosis and exosmosis, not yet, however, as well investigated, as are the corresponding phenomena in two liquids, or two gases. Of the reality of this action there is no doubt, as it may be imitated out of the body. Returning from the lungs into the left auricle, and so into the strong left ventricle, and regurgitation being prevented as on the right side by similar curious valves, the blood is forced into all parts of the body, to nourish it, and generate animal heat; again to return, having lost its bright colour and excess of oxygen, by the veins, to the threshold of the heart, whence we set out. Much has been written as to the dynamic cause of the return of the blood by the veins. Parry's experiments would seem to show that these are quite passive agents, though many attribute muscular fibres to some of them; apparently the most efficient cause is a vis-a-tergo derived from the capillaries,* and perhaps connected with their nutritive action. This is aided by the beautiful valves of the veins,† and somewhat perhaps by the pulsation of the arteries which they commonly closely accompany, also by the general elasticity of the tissues, the action of the muscles, and the suctional power of the thorax and heart, as demonstrated by Barry. The power of the ventricles, aided by that of the arteries, is, at the least, great enough to account for the flow from the heart to the capillaries; but pulsation only occasionally extends to the veins in some cases of inflammation; and we see no pulsation in the capillaries under the microscope, though sometimes a

* From a similar cause the thoracic duct has burst when it has been tied on the living animal.

In the lacteals and lymphatics the numerous valves must be principal agents in aiding the movement of the chyle and lymph.

sort of oscillation, as mentioned by Bichat. In the lower animals we, many years back, noticed that the vessels which circulate their fluids effect the same by means of parietal vibratile cilia.* We must, however, in the higher animals, set down the venous flow, principally to the impetus from the capillaries. With respect to absorption, Barry attributes it to the power of the suction above alluded to, and its attendant atmospheric pressure, and explains on the same views the efficacy of cupping in preventing the absorption. of poisons from wounds and venomous bites. With respect to the arteries, it appears that the galvanising or stimulation of the nerves distributed to their coats, causes an increase of action in them, and, according to Soemmering, those of middle size are best supplied with nerves. We see nervous impressions evidently influence the circulation of parts; and the small vessels, when cut in operations, often spout out with a considerable force, apparently intrinsic.

The mechanism, or supposed mechanism, of the circulation early obtained the notice of philosophers; but before our Harvey it appears that no anatomist had a correct and complete knowledge of it. Nemesius, whom we translate from Portal, observes :-"The pulse commences at the heart, principally in the left ventricle of that viscus. The artery dilates and contracts with violence, and in a regular and harmonious manner. In dilatation it draws from the neighbouring veins the thickest portion of the blood, the exhalations from which serve to repair the vital spirits. In . contraction it distributes over all the body, by unseen routes, all the exhalations which it contains, as the heart in expiration throws off all that is fuliginous either by the mouth or the nose." Here we may have, in obscure language, the distribution of the blood by the left ventricle to the body, and perhaps the return of the blood. The circulation through the lungs seems alluded to, but that through the liver is passed over in silence.

Servetus attributed animal heat to the circulation; was Report of the Trans. of the Brit. Assoc., 1839.

aware that the heart receives venous blood from the liver, that it is then passed through the lungs, gets to the left ventricle, and is distributed to the body by the arteries. He also gives reason for his belief in the circulation, observing that Galen was unacquainted with the important truth. He denies the old doctrine that the blood passes from the right to the left side of the heart through the septum of the ventricles, noticing the size of the pulmonary arteries, and that they proved the pulmonary circulation. With these truths, however, he appears to mix a doctrine of natural, animal, and vital spirit, and is not very intelligible on some points.*

Vesalius was probably acquainted with much of the circulation, but not with that of the portal system; he noticed the effect of ligatures on vessels, one side being distended, the other empty. Galen understood the generation of animal heat as dependent on the circulation; that the arteries contained blood and not air, a common idea with the early anatomists; he knew too the vena porta, and the systole and diastole of the heart; also the foramen ovale in the fœtal heart, that opening between the two sides to exclude the pulmonary tract from the circulation in a being not yet breathing. Columbus and others knew perfectly the valves and mechanism of the heart, and the course of the blood through the lungs (as did Servetus, from the ample size of the pulmonary artery), but not, apparently, the systemic circulation, nor that through the liver. Ruef's claims are exposed by Portal. Many, Cesalpinus for instance, thought there was a to-and-fro motion in the arteries. Fabricius, the master of Harvey, must have been instrumental in leading the way to the full discovery of this phenomenon, by his beautiful account and delineation of the valves of the veins. Of all these earlier anatomists, however, Servetus perhaps, is more particularly entitled to be mentioned with Harvey, and happier had he been had he confined his studies to anatomy, instead of embarking in what has been * From Pettigrew and Portal's extracts from his rare work.

Harvey

termed the anti-pacific ocean of controversy. seems himself alone entitled to the honour of being considered the discoverer, describer, and demonstrator of the circulation. The labours of Willis, Senac, and Tiedemann, and of later anatomists, particularly those of our own country, have fully worked out this portion of anatomy, especially as relates to a practical knowledge of the bloodvessels.

There are a few glands or glandlike bodies-the thymus, thyroid, and super-renal capsules, ductless like the spleen, and respecting which there is the same obscurity of function. At present they are rather considered to be appendages of the absorbent system, and concerned in changes necessary to the formation of the blood. There are some peculiarities, as, for instance, the period of their greatest development, which may tend to throw light upon their nature. For instance, has the thymus any connexion with lactation, the thyroid any sympathy with the mamma? Probably it is to comparative anatomy that we must look for a solution of these difficulties, particularly to the laws of development and principle of analogues.

But there are, besides the intestinal rejectamenta, other impurities to be thrown out, and that from the blood itself, for instance, superabundant salt, water, and that nitrogenous product derived from the waste of nerve, muscle, &c., or urea. This is accomplished by the kidneys, investigated by Galen and Eustachius, and minutely and satisfactorily studied by modern histologists, particularly by Mr. Bowman, as they were by Ruysch and Malpighi, by means of injection.

With respect to the brain and nerves, the medium of the impulse of the mind upon the body, and vice versa of the body upon the mind-without which we could have no manifestation of feeling, thought, sensation, or motion-we must say, on the threshold of the subject, that though we are acquainted with this portion of anatomy, even to the

* Harvey's work was addressed to his Prince, Charles I., in a most courtly allegorical dedication,