400 ANATOMICAL AND PATHOLOGICAL OBSERVATIONS. 



to protect the delicate villi from the matters contained in the 

 bowel. They had thrown off their protective epithelium 

 when required to perform their functions, just as the stomach 

 had done to afford gastric juice, and the intestinal follicles to 

 supply their peculiar secretions. In the intervals of diges- 

 tion the epithelium is rapidly reproduced. 



The germinal membrane, which, as I have stated, not 

 only forms the outer membrane of the follicles, under the 

 epithelia, but also the underlying membrane of the villi, 

 contains in its substance germinal centres of an oval form, 

 situated at pretty regular distances. From these the epithe- 

 lium appears to be reproduced during the intervals of absorp- 

 tion, as stated in the first chapter. 



During this process of development, the primary mem- 

 brane appears to split into two laminae, the epithelia passing 

 out from its nuclei between these. This would account for 

 the epithelia, particularly the prismatic and conical, adhering 

 by their free extremities. 



Such are the processes which would appear to take place 

 in the villi of the intestinal tube during digestion and absorp- 

 tion. When considered in relation to the functions of digestion 

 and absorption of chyle, these processes are highly interesting. 



The labours of the chemist have now so far simplified the 

 theory of digestion, as to deprive the stomach of the vitalis- 

 ing or organising powers so long ascribed to it. 



Every step in this chemico-physiological inquiry leads to 

 the conclusion, that the changes which the food undergoes 

 while in the cavity of the gut are entirely of a chemical 

 nature. 



If we continue, then, to apply the term digestion to that 

 series of processes by which the aliment is assimilated to the 

 matter of which the body is composed, we must divide the 

 series into two groups. The first group will include all those 

 changes which take place within the digestive tube, but ex- 



