172 Mr John Guodsir on the Structure of the Intestinal 



beneath it, as in glands. Serous membranes have a similar 

 constitution. 



These nuclei I have elsewhere shewn to be germinal spots 

 or centres of reproduction and growth in the secreting glands 

 {lac. cit.). More extended observation has convinced me that 

 they are the centres from which all epithelium, whether se- 

 creting or protective, is formed. The process is similar to 

 that described by Reichart and Dr M. Barry, as taking place 

 in the ovum. Cells form in the centre of the spot. These cells 

 increasing in size, and having other cells in their interior, 

 pass off in a radiating direction in the plane of the primary mem- 

 brane, and gradually assuming the form and properties of the 

 epithelium of the region, till they meet and ^orm a continu- 

 ous layer of nucleated particles which cover the primary 

 membrane, from whose nuclei they sprung. These nuclei still 

 remain as sources of future crops of epithelia. 



During this process of development, the primary membrane 

 would appear to split into two laminae, the epithelia pass- 

 ing out from its nuclei between these. This would account 

 for the epithelia, particularly the prismatic and conical, adher- 

 ing by their free extremities. 



Such are the processes which would appear to take place in 

 the villi of the intestinal tube during digestion and absorption. 

 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 their vital- 

 izing or organizing 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 na- 

 ture. 



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 sc- 

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

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

 terior to the organism. The second will include those which 

 present themselves after the alimentary matter is taken up into 

 the animal body, and becomes buried in its substance. The 



