400 



STOMACH AND INTESTINE. 



may conjecture that its absorptive powers are 

 chiefly intended to be exercised on the water 

 of its contents ; and on the sugar and lactic 

 acid produced by that slow metamorphosis, 

 which dense starchy substances would here 

 continue to undergo. But in animals like 

 the Horse, whose aliment passes quickly 

 through the stomach and small intestine into an 

 enormous colon, it is difficult to avoid believ- 

 ing, that a more or less modified gastric juice 

 accompanies the insoluble albuminous com- 

 pounds of the food into this segment of the 

 canal, and continues its solvent action during 

 their long sojourn in its interior. It would 

 otherwise be almost impossible to explain the 

 nutrition of such animals. How far the 

 large intestine can take up fat remains un- 

 known. But it seems certain that its share in 

 the absorption of this alimentary principle is 

 very slight compared with that of the small 

 intestine. 



The entire process of digestion might there- 

 fore be described as consisting in the applica- 

 tion to the food of a variety of agencies, such 

 as mechanical division, solution, and metamor- 

 phosis. In whatever manner these are ap- 

 plied (either to the food as a whole, or to the 

 several alimentary principles which form its 

 constituents), and whether they operate in suc- 

 cession or combination in any case, they all 

 work towards the same object : namely, that 

 of preparing the food for absorption by the 

 vessels and lacteals which occupy the walls 

 of the digestive canal. With this act of ab- 

 sorption, the function of digestion terminates. 



The chief agents of this process of division 

 and solution, we have found to consist of 

 certain liquid secretions ; which are poured 

 into the canal, either by the ducts of several 

 glands, or by the vast compound mucous mem- 

 brane that lines the various parts of its cavity. 

 In short, the food received into the intestinal 

 tube, mingles with a large quantity of a mixed 

 fluid ; which itself represents the aggregate 

 contributions of the salivary glands, the 

 pancreas, the liver, the stomach, and the in- 

 testine. 



But the more accurate researches which 

 have recently been made on the nature and 

 amount of these secretions, confirm a suspi- 

 cion that has long been entertained with 

 respect to some of them by physiologists. 

 Comparing their quantity and quality with that 

 of the faeces and the food, we can now confi- 

 dently state, that but a very small fraction of 

 their whole mass leaves the canal with the 

 excrements ; by far the greater part of it 

 being reabsorbed into the vessels of the ali- 

 mentary canal. 



This proposition so important to a cor- 

 rect appreciation of the true office of the in- 

 testinal canal, and of the relation of digestion 

 to nutrition has lately been placed in the 

 clearest light by the admirable researches of 

 Bidder and Schmidt upon animals. From 

 their toilsome and accurate experiments, it 

 would appear, that the total quantity of matter 

 which thus leaves and returns to the cir- 

 culation of an adult man, may be esti- 



mated at little less* than 20 pounds of liquid 

 daily ; of which about 3 per cent, consists of 

 solids in solution. The importance of these 

 " recrementitious " secretions to the system, is 

 well shown by the results which follow the 

 establishment of an artificial biliary fistula. 

 Unless the ensuing loss of bile is compen- 

 sated by the digestion of a much larger quan- 

 tity of food, the animal so operated on soon dies 

 of inanition. And it is probable that the ex- 

 haustion produced by diarrhaea, or by the 

 discharge of the intestinal contents through 

 an abnormal opening in the bowel, may be 

 partially due to a similar loss of this and other 

 rich organic fluids, which ought to be reab- 

 sorbed. 



Whether the secretions experience any 

 change prior to absorption whether any of 

 them are really modified, and thus far digested 

 by their colleagues remains at present in 

 doubt. It may be conjectured, however, that 

 they are so altered. At any rate, it would 

 seem that, by provoking these secretions f, 

 the whole system of a starving animal may 

 be for a time invigorated and restored. But 

 the chain of these phenomena is at present 

 too indistinctly seen, and their connection 

 with various other organic processes much too 

 obscure, to justify us in doing more than offer- 

 ing this conjecture, as one of the most imme- 

 diate explanations of certain well-known facts. 



But we know enough to state that, within 

 the limits of ingestion and egestion, lie two 

 corresponding acts of absorption and secre- 

 tion. Each of these is, so to speak, the co- 

 efficient of two elements. Absorption takes 

 up food and secretions : secretion pours out, 

 not only materials newly devoted to this 

 purpose by the system, but others which have, 

 in all probability, already subserved it many 

 times before. The great mass of the intesti- 

 nal secretions is thus continually revolving in 

 a cycle : forming a circulation the channel of 

 which, placed in the intestinal canal, leaves 

 and returns to the blood that flows in its 

 walls ; and only allows a very small offshoot 

 of its current to reach the outer world, bear- 

 ing with it certain of its effete particles. 



The important chemical details of this cir- 

 culation have yet to be won by sedulous and 

 thoughtful " questionings of nature." But 

 since, for the acquisition of such results, the 

 liver offers what will probably be the easiest 

 prize, it may be useful to point out how little 

 even the vast progress of modern chemistry 

 has hitherto been able to establish respecting 

 its true physiological import. The portal blood, 



* From the greater proportionate waste of small 

 animals, it is possible that this estimate (22 Ibs. for 

 an adult weighing 140 Ibs.) is rather too large. 



f Some of the American Indians are alleged to 

 eat clay with the object of allaying hunger. The 

 drinking of water is well known to have a similar 

 effect, and has been shown to increase the quantity 

 of these secretions without causing a converse dimi- 

 nution of their density. And the benefit which a 

 starving person derives from the minutest portion 

 of food is sometimes so sudden and remarkable, 

 that we can scarcely avoid referring it to the same 

 explanation. (Compare 1 Sam. xiv. 27. 29.) 



