ON EMBRYONIC DIFFERENTIATION 271 



the larger bowel, and which must, necessarily, be connected 

 with the digestive phenomena occurring therein. 



The operation of the law of gravitation, furthermore, 

 keeps the caecal contents in a position, favourable for 

 admixture with the secretion of the appendix (see Fig. 1 1 3), 

 ere they mount the lumen of the ascending colon, and 

 pursue their course along the remainder of that bowel. 

 It is here, in particular, where the most characteristic 

 stercoraceous changes are effected in the alvine contents,. 



FlG. us;. VIEW OF THE ILEO-COLIC VALVE FROM THE LARGE INTESTINE. 



\ (After San torini.) 



The figure shows the lowest part of the ileum, /, joining the caecum, c, and the 

 ascending colon, o, which have been opened anteriorly, so as to display the ileo- 

 colic valve ; a, the lower, and e, the upper segment of the valve. 



but whether these changes are due to ordinary local 

 chemico-physical action alone, or whether this is aided, by 

 anaerobic bacterial activity, it would be premature to 

 speak, still it would seem, not too far-fetched to say, that 

 here the alimentary residuum may perhaps, in order to 

 effect its complete physical disintegration and chemical 

 resolution, in addition to the action of the local bowel 

 digestive agencies, have added a living bacterial agency 

 or " pseudo-phagocytic " organisation, on kindred lines to 

 those of the leucocytes, or white blood corpuscles, in the 

 economy of nutrition. The presence here, of organisms 

 of this character, in ordinary physiological conditions of 



