But, whatever conclusion we may be induced to form respecting the office of the veins, or the share

.

would be most satisfactory, could we prove that no rupture or extravasation had taken place; but in consequence of the perpetual liability to such accidents, it must be regarded as of a very equivocal nature. The analogy of the lymphatics with the lacteals, and the effect of the absorption of deleterious substances, are the proofs on which Hewson principally rests his opinion. This circumstance is also insisted upon by Cruikshank, who remarks, that in the absorption of poisons, it is the lymphatics, and not the veins, that are inflamed; On the Absorbent System, p. 28. A remark of the same kind is made by Mr. Bell; Anat. v. iv. p. 303, he says, indeed, that the veins do occasionally become inflamed, but that they are much less liable to inflammation than the lymphatics. It has been urged, as a proof of absorption being carried on by the lymphatics, that this process continues for a considerable time after the circulation has ceased. Bichat limits this period to two hours; ubi supra, t. ii. p. 118; but it is supposed by many anatomists to remain for a considerably greater length of time. It is necessary to observe, that although M. Magendie conceives that the lacteals have the power of absorbing chyle, and probably are the principal agents in this operation, yet he performed a series of experiments, in conjunction with M. Delille, the results of which convinced him that the mesenteric veins also possess this power; see Journ. Physiol. t. i. p. 23. et seq; also, Elem. Physiol. t. ii. p. 183..5. The experiment consisted in detaching a portion of the small intestines from the remaining part of the canal, in dividing all its lacteals and its blood-vessels, except one artery and one vein; a deleterious fluid was then injected into the divided intestine, and after a certain interval, the effects of the poison were manifested in the system. Without intending to throw the least reflection upon the fidelity of the narrator, or the skill of the experimentalist, I cannot but remark, that I conceive, in so complicated an operation, it would be impossible to guard against various sources of inaccuracy,

which they possess in absorption, it appears a wellestablished principle, that the only use of the lacteals and the lymphatics, is to absorb certain substances that are presented to their orifices; it will it will now, therefore, remain for us to inquire, what is the distinctive function of each of these systems of vessels, or what is the nature of the substance which they each of them respectively absorb? With regard to the lacteals, the question is easily answered; the only substance which they are destined to receive, is the chyle; and they appear to be the only vessels which are ever employed in conveying this substance from the intestines, where it is produced, to the thoracic duct.

We may,

that would essentially interfere with the inference that we must draw from the experiment.

5 It is not intended, by this observation, to deny absolutely that extraneous substances are never, under extraordinary circumstances, admitted into the lacteals. The earlier experimental physiologists generally agreed, that colouring substances might be detected in the chyle; this was especially the case with Lister and Musgrave's experiments on indigo; Phil. Trans. for 1683, No. 143. p. 6; and for 1701, No. 270. p. 819. No. 275. p. 996; and, what is more important, their results were confirmed by Haller; who informs us, that he repeated the experiments with success; El. Phys. xxiv. 2. 3. This is also stated as the result of J. Hunter's experiments; Med. Comment. p. 44. et seq.; and Cruikshank assents to the opinion; On the Absorbents, c. 8. But it is generally agreed that the power of these vessels in admitting the introduction of extraneous substances is very limited; and the late experiments of MM. Magendie, Flandrin, and Dupuytren, tend to show, that even this very limited power does not exist; see Physiol. t. ii. p. 168, 9; where it is stated, as the result of direct experiment, that when alcohol, camphor, &c. are mixed with the food, the sensible properties of these substances

therefore, consider the lacteals as the immediate agents in nutrition, by which the matter, after being duly

are detected in the blood, but never in the chyle. These experiments, I may observe, are directly opposed to those of Hunter; while, on the other hand, we are informed, that they agree with, the results which had been obtained by Hallé; see Fouréroy, Syst. v. x. p. 91. We have also a similar kind of experiment stated in a general way, in the Edinburgh Med. Journ.v.xix. p. 154,5; where a quantity of starch and indigo was confined in a portion of the intestine, when it was found, upon examination, that none of it had entered the lacteals. We have, also, a very elaborate train of experiments by the active and intelligent physiologists, Tiedemann and Gmelin, which appear to have been conducted with great attention to every circumstance that might affect their accuracy, the results of which confirm the conclusions of M. Magendie. Their object was to ascertain whether any direct communication exists between the digestive organs and the blood-vessels, except through the route of the lacteals, and the thoracic duct. The experiments consisted in mixing with the food of certain animals, various odorous, colouring, and saline substances, which might be easily detected by their sensible or chemical properties, and, in comparing, after a proper interval of time, the state of the chyle with that of the blood in the various mesenteric veins. The odorous substances employed were camphor, musk, alcohol, oil of turpentine, and assafœtida; these were generally found to be retained in the system, so as to be detected in venous blood, and in the urine, but not in the chyle. The colouring matters were sap-green, gamboge, madder, rhubarb, alkanet, and litmus; these appeared, for the most part, to be carried off without being absorbed; while the salts, viz. potash, sulphuro-prussiate of potash, muriate of barytes, muriate and sulphate of soda, acetate of lead and of mercury, and prussiate of mercury, were less uniform in their course. A considerable portion of them seemed to be rejected, while many of them were found in the urine, several in the venous blood, and a very few only in the chyle. Hence the authors conclude, that

elaborated in the digestive organs, is transmitted to the blood, for the purpose of being assimilated to this fluid, and finally employed in repairing the waste that is necessarily occasioned by the separation of the various secretions.

With respect to the lymphatics, although it would appear that they, at all times, contain a greater or less quantity of the transparent fluid, from which their name is derived, yet we have reason to suppose that their contents are of a more miscellaneous nature than those of the lacteals. If we adopt the Hunterian hypothesis, we must suppose that all the constituents of the body, as well as a variety of other substances, which are either intentionally or accidentally placed in contact with the extremities of the lymphatics, are capable of entering into them, and of being conveyed along them to the thoracic duct. And if we embrace the opinion of M. Magendie, that the function of absorption is divided between the lymphatics and the veins, or even principally carried on by the latter, there are many morbid phenomena, which seem to prove that extraneous bodies of various kinds are capable of passing along them. How far the substance

the odorous and colouring substances never pass into the lacteals, and that saline bodies do so occasionally only, or perhaps incidentally; the whole of them are, however, found in the secretions, and they must, therefore, have entered into the circulation by some other channel than the lacteals; Edin. Med. Journ. v. xvii. p. 455. et seq.

6 It is obvious that, upon the hypothesis of M. Magendie, this variation will not take place in the contents of the lymphatics,

which is conveyed by the lymphatics may occasionally serve for the purposes of nutrition, it is not, perhaps, very easy to ascertain; but we may venture to assert that nutrition is not their sole, or even their primary function. This, we can scarcely doubt, is the appropriate office of the chyle; and although it may be

or at least in a much less degree. And it must be admitted that the properties of the lymph seem to be more uniform than might have been expected, had it been composed of, or formed from, all the different constituents of the body. According to M. Magendie, it bears a strong analogy to chyle, especially in the characteristic property of separating by rest into two parts, one more solid and fibrous, and another which remains fluid, and more resembles albumen; Physiol. t. ii. p. 171, 2. M. Chevreul has given the following analysis of the lymph of a dog; ibid. p. 173:

Mascagni, however, says, that the lymph is not uniform in all parts, but that it partakes of the properties of the contiguous substances, bile, fat, &c. Vas. Lymph. Hist. p. 1. § 4. p. 28, 9. A similar opinion is maintained by Blumenbach, Inst. Physiol. § 438. p. 237. Hoffmann's Observations on the Lymph, considering the period when they were written, are not without their value; Med. Rat. lib. i. § 2. ch. iii.