216 



NUTRITION 



Internal nutrition is the portion of this general function that has to do 

 with the passage of the blood's nutrients into the tissues and of the tis- 

 sues' waste back into the blood. Both parts of each of these processes 

 are indispensable to life. Of external nutrition the first process is absorp- 

 tion. 



FIG. 113 



The periglandular and the villous plexuses of nerves in the gut of the porpoise: a,c,f, 

 triangular and stellate cells; b, d, e, fusiform cells. (Ramon y Cajal.) 



FIG. 114 



Section in the wall of the small gut of the eel-pout. The arteries are shown in black, the 

 veins cross-striated, and the lymphatics granulated. (Melnikow.) 



ABSORPTION. 



Absorption is the process by which food is conveyed directly or in- 

 directly into the circulating blood from the alimentary canal. From the 



