INTESTINAL DIGESTION. 



433 



with the amount of the secretion by whose agency this preparation is specially 

 affected ; and as there are many indications that the quantity of each that is 

 taken up in absorption is limited, and that it bears a relation to the wants of 

 the system, it is probable that the amount of the solvent or reducing fluid that 

 is secreted by each glandular apparatus is regulated (as we have seen it to be 

 in the case of the gastric juice, 444) by the demand set up by the nutrient 

 operations, rather than by the amount of alimentary matter that is waiting to 

 be digested. The processes of digestion and conversion are probably continued 

 during the entire transit of the alimentary matter along the small intestine, 

 and at the same time the products of that conversion are gradually being with- 

 drawn by absorbent action ; so that, by the time it reaches the caecum, the 

 undigested residue contains little else than the innutritions or insoluble compo- 

 nents of the food, together with the excrementitious portion of the bile and of 

 other secretions. Up to this time, the contents of the canal have an alkaline 

 reaction; but in the caecum they again become acid; and it has been supposed 

 that this change depends upon the secretion of a fluid analogous to the gastric 

 juice, by the large and numerous tubular glands contained in the parietes of this 



t, whereby the albuminous matters still undigested might be more completely 

 solved. This supposition appeared to derive weight from the fact, that the 

 caecum is peculiarly large in most Herbivorous animals, the " appendix vermi- 

 formis" being also of greatly increased dimensions, and sometimes double. But 



Fig. 127. 



Fig. 128. 



A section of the small Intestine containing some 

 of the glands of Peyer, as shown under the micro- 

 scope. These glands appear to be small lenticular 

 excavations, containing, according to Boehm, a white, 

 milky, and rather thick fluid, with numerous round 

 corpuscles of various sizes, but mostly smaller than 

 blood-globules. The meshes seen in the cut are the 

 ordinary tripe-like folds of the mucous coat, and not 

 the venous texture spoken of under the follicles. 



Portion of one of the patches of Peyer's Glands, 

 from the end of the Ileum, moderately magnified ; 

 the villi are also displayed. 



from the experiments and observations of Blondlot, it seems probable that the 

 acid of the caecum is rather a product of the transformation of saccharine sub- 

 stances in the alimentary canal, than a secretion from its walls. 1 Still, as this 

 lactic acid has a solvent power for albuminous matters, which is equal, or nearly 



28 



1 See his "Traite" analytique de la Digestion," p. 103. 



