We are informed, however, by M. Magendie that experiments have been performed by him self and by M. Flandrin, which afforded directly contrary results, and that these experiments were so frequently repeated, and varied in such a manner, as to leave no doubt of their accuracy.* We have here the opposing testi mony of individuals, both of them of the highest authority in science, and eminent for their skill in experimental research. From personal considerations it might be difficult, if not impossible, to decide between them ; but when we take into account the circum stance that the experiments of MM. Magendie and Flandrin were executed subsequently to those of Hunter, and with the benefit of his experience and that of the improved state of the science during the last half century ; when, moreover, we are informed that the experiments of the French physiologists were more nu merous than those to which they were opposed, and that their results were uniform and un equivocal, we can scarcely refuse our assent to the conclusion, that the experiments of John Hunter do not a sufficient foundation for the doctrine of the non-absorption of the veins.
But the French physiologists have not sa tisfied themselves with repeating the experi ments of Hunter ; they have extended them in various ways, and have obtained results supposed to be still more decisive in favour of venous absorption. Among the most im portant, or at least the most curious of these, is an experiment which was performed by M. Magendie, in conjunction with M. Delille, and which was conceived by these physiolo gists to afford the most unequivocal proof of their hypothesis. It consisted in dividing all the parts of one of the posterior extremities of a living animal except the artery and the vein, and in applying to the foot a poisonous substance; when, in the short space of a few minutes, ;he effects of the poison on the func tions of the animal were most distinctly ap parent.* It was argued that in this case there was no mode of communication by which the poison could be conveyed from the extremity to the centre of the system except the vein, and that, therefore, the vein must have acted as the absorbing vessel. The experiment was rendered more striking, and, as was conceived, more conclusive, by dividing the bloodvessels themselves and introducing metallic tubes between the divided ends, through which alone the two currents of the 'arterial and venous blood respectively could pass in forming the communication between the extremity and the trunk of the animal, yet, under these appa- • rently unfavourable circumstances, the delete rious effects were manifested on the system as in the former Experiments of this description appear to have been sufficiently multiplied to establish the fact, that the poison in these cases passed along the vein, and was conveyed in the general mass of the blood.
The result of these experiments is no doubt very remarkable, and what would scarcely have been anticipated ; yet we may remark, that there is one circumstance connected with them, which, in a great measure, invalidates the conclusion that has been supposed to follow so necessarily from them. It may be inferred from the expression made use of, that the poison employed, which was the extract of the upas tree, was inserted by a puncture or incision into the foot of the animal, and would, therefore, in the first instance, be mixed with the blood ; so that the only deduction which we are warranted to draw from the experiment is, that the venous blood, being infected with the poison, had the power of communicating the infection to the system at large.T On this
view of the subject we should not regard the above as a case of absorption, but merely as an instance of the power of extraneous sub stances, under certain circumstances, of uniting with the venous blood and retaining their specific properties.
In connexion with these experiments of M. Magendie and his associates, we have another series which were performed by MM. Tiedemann and Gmelin, and which bear di rectly upon the question of venous absorption. Their object was to ascertain whether there was any direct communication between the organs of digestion and the bloodvessels except by means of the lacteals. For this purpose they mixed with the food of an animal various substances, which by their colour, odour, or other sensible and physical properties, might be easily detected in the fluids of the body. After some time the animal was examined, and the result was that unequivocal traces of the substances were not unfrequently detected in the venous blood and in the urine, while it was only in a very few instances that any in dication of them could be discovered in the chyle. The colouring matters employed were various vegetable substances, such as gamboge, madder, and rhubarb ; the odorous substances were camphor, musk, assafcetida, &c. ; while, in other cases, various saline bodies, such as muriate of barytes, acetate of lead and of mercury, and some of the prussiates, which might be easily detected by chemical tests, were mixed with the food. The colouring matters, for the most part, were carried out of the system without being received either into the veins or the lacteals ; the odorous substances were generally detected in the venous blood and in the urine, but not in the chyle, while of the saline substances many were found in the blood and in the urine, and a very few only in the chyle' The conclusion, which we are disposed to regard as the fair inference, from the facts and arguments that have been adduced on the subject of venous absorption, is that, although there are strong analogies and various patho logical considerations which would induce us to confine the function of absorption to the lacteals and the lymphatics, yet that the result of the experiments, although not uniform, is upon the whole in favour of venous absorption. It only remains for us to inquire how far the state and actions of the parts on which the experiments were made, were so far neces sarily deranged by the process to which they were subjected as to render the results inapplicable to the natural condition of these organs. Now this certainly appears to be the case in the experiments of MM. Magendie and Delille, where the poisonous substance was introduced into the blood ; and the same remark may probably be applied to a number of pathological occurrences that have been supposed to afford a proof of venous absorp tion, such, for example, as the case of ulcerated surfaces, where pus has been detected in the veins, and still more extraneous bodies, which may have been either accidentally or designedly inserted into the ulcerated part.t But it is not unreasonable to suppose that in these in stances, in consequence of the erosion arid partial destruction of the organs, the small branches of the veins will present an external orifice, through which the pus or other ex traneous substance may be immediately re ceived into the sanguiferous system, nearly upon the same principle as in the experiments related above.