DIGESTION. 



21 



hypotheses and conjectures have been formed 

 on the subject, there is none which seems to 

 have obtained any credit with physiologists, or 

 indeed to be entitled to much consideration.* 

 The latest researches on the subject are those of 

 Home, and of Tiedemann and Gmelin. Home 

 examined the structure of the spleen, and, as the 

 result of his investigation, informs us that it 

 consists entirely of a congeries of bloodvessels 

 and absorbents, and that there are interstices 

 between the vessels into which the blood is 

 effused, through certain natural orifices in the 

 veins, when they are much distended. The 

 conclusion which he forms respecting the use of 

 the spleen is, that it is a reservoir for any super- 

 fluous matter, which may exist in the stomach, 

 after the process of digestion is completed, 

 which is not carried off by the intestines, as 

 serum, lymph, globules, and mucus; that these 

 are conveyed to the spleen by certain communi- 

 cating vessels, and are removed from it, partly 

 by the veins and partly by the absorbents.-)- 



The account of the structure of the spleen 

 which is given us by Tiedemann and Gmelin 

 is considerably different from that of Home. 

 They inform us that it essentially resembles 

 that of the lymphatic glands, and they conceive 

 that it is to be regarded as an appendage to the 

 lymphatic system. They suppose its specific 

 function to be the secretion of a fluid which is 

 conveyed to the thoracic duct, and being united 

 with the chyle, converts it into blood. J There 

 are many circumstances which render it pro- 

 bable that the spleen, in some way or other, 

 promotes sanguification, and we have some 

 reason to believe, that there is an immediate 

 and a ready communication between its arterial 

 and its absorbent systems, but we conceive 

 that the hypothesis must still be regarded rather 

 as a plausible conjecture, than as a deduction 

 from facts. 



There is moreover a circumstance which 

 must not be overlooked in our speculations 

 respecting the spleen, that we have some well 

 authenticated cases, where it has been either 

 originally wanting, or has been removed from 

 the body without apparent injury . This argu- 

 ment cannot, however, be considered as decisive, 

 because it is well known, that in consequence of 

 the extraordinary compensating powers of the 

 system, certain organs may be occasionally dis- 

 pensed with, which, under ordinary circumstan- 



Sec Haller, El. Phys. lib. xxi. ; Scemmering, 

 t. vi. p. 149 et seq. 



t Phil. Trans, (or 1808, p. 46 et sea. and p. 133 

 et scq., and for 1821, p. 35 et seq. pi. 3. .8. 



$ We have an ample and apparently correct ab- 

 stract of the memoir of Tiedemann and Gmelin in 

 the Ed. Mcd. Journ v. xviii. p. 286 ct seq. See 

 also on this subject Elliouon's Physiol. p. 108 et 

 cq. ; also an essay by Dr. Hodgkin, appended to 

 his translation of Edwards'* physiological work. 



liaillie's Morbid Anat., p. 260, 1; works, by 

 Wardrop, v. ii. p. 235. [Dupuytren observed an in- 

 creased voracity in dogs from which the spleen had 

 been removed. Assolant, Dissertation du Kate ; and 

 Mayo has in two instances remarked a considerable 

 obesity in dogs after the removal of the spleen, 

 but does not say whether this may not be attribu- 

 table to the increase in the quantity of their food. 

 In both instances the duration of the obesity was 

 for leu than a year. Mayo's 1'alhol. vol. i. ED.] 



ces, appear the most essential to its existence 

 and welfare. We may therefore conclude with 

 respect to the pancreas and the spleen, th:it 

 although there is reason to suppose that they 

 contribute, in some way, to the function of di- 

 gestion, we are still unable to ascertain the pre- 

 cise mode in which they conduce to this end. 



Before we dismiss this part of our subject, it 

 will be necessary to make a few observations 

 upon a question, which has been proposed in 

 relation to the digestive process, whether any 

 part of the aliment passes through the stomach, 

 and is taken up by the absorbents, without de- 

 composition. It is obvious that this cannot be 

 the case with vegetable substances of any des- 

 cription, and with respect to substances of ani- 

 mal origin, that form a part of the diet, although 

 they approach so much nearer to the nature of 

 chyle, yet it appears that they are not entirely 

 identical with it, and that they must conse- 

 quently be decomposed and assimilated to the 

 general mass, before they can serve for the pur- 

 poses of nutrition. There are indeed certain 

 substances, that are received into the stomach, 

 which would appear to form exceptions to this 

 general principle ; these are the various saline 

 substances, which are found in all organized 

 bodies, as well as some others, which give their 

 appropriate odours and flavours to the food, and 

 also certain medical agents. There are some 

 salts, which appear to constitute an essential 

 part of the blood and other animal fluids, and 

 as the same salts are introduced into the sto- 

 mach with the food, we may conceive that 

 they pass unchanged into the vessels. There 

 are likewise certain substances which give their 

 specific odour to the milk, and to other secre- 

 tions and excretions, proving that they likewise 

 pass into the circulating system without suffer- 

 ing decomposition, and the same is the case 

 with some of the medicaments.* 



IV. Theory of digestion. We now enter 

 upon the fourth branch of our inquiry, the mode 

 in which we are to explain the action of the di- 

 gestive organs upon the aliment. This has been 

 one of the most fertile sources of conjecture and 

 speculation from the earliest period, from Hip- 

 pocrates down to our own times, and the ques- 

 tion is one respecting which the greatest differ- 

 ence of opinion still exists among the most 

 intelligent physiologists .( We shall not think 

 it necessary to notice the opinions of the older 

 writers, which were necessarily formed from 

 very insufficient data, but shall select those hy- 

 potheses which appear deserving of more par- 

 ticular attention, either as having been supported 

 by men of acknowledged eminence, or as 



See the remarks of Fordycc, p. 122, 3 ; the 

 results of the experiments that have been made on 

 this point are somewhat contradictory ; but upon 

 the whole there seems no doubt that, under certain 

 circumstances, various extraneous substances may 

 be taken up by the absorbents and recognized in 

 the blood and other fluids. See Bostock's Physiol. 

 v. ii. p. 569, 0, note. 



t For an account of the doctrines maintained by 

 the earlier physiologists, the reader is lefi-rrrd to 

 the treatise of Kernel, De Concoctionibm, Physiol. 

 lib. vi. cap. 6 ; Bocrhaave, Praclect. not. ad $ 86 ; 

 Hallcr, El. Phys. xix. 4 et 5 passim ; and Blu- 

 mcnbach, Instit. Physiol. 360. 



