ASSIMILATION 



83 



mxt 



Inl. 



stomachs of young milk-feeding animals, has a coagulating effect 

 upon milk, and also digests milk protein or casein. The lipase 

 of the gastric juice acts princi- 

 pally upon lipins and emulsified 

 fats, splitting them into glycerol 

 and fatty acids. As the acidity 

 of the stomach contents increases, 

 the pyloric sphincter relaxes at 

 intervals, permitting the expulsion 

 of the partially digested food 

 mass from the stomach into the 

 small intestine. 



The muscular activities of the 

 small intestine are of two types, 

 known as peristalsis and segmen- 

 tation (Fig. 48). In peristalsis, a 

 contraction begins at the upper 

 end of the intestine and passes 

 with wave-like effect toward the 

 lower end. This motion has a 

 tendency to cause the passage of 

 the food mass toward the large 

 intestine. Segmentation, on the 

 other hand, consists of a series 

 of contractions occurring close yig. 47.— The digestive tract and 

 together and simultaneously at appended structures of the frog, 

 different levels of the intestine. b.c, buccal cavity; b.d., bile dwt-. 

 This results in the pinching of " • """^^^ j''^*^^"''^ '•'^- '''''"' ^'!"''' 



'^ cL, cloaca; du., duodenum; e., position 



the food mass into segments; and of eye; es., esophagus; E.I., Eustachian 



since these segmentation con- ^^^e; o.b., sail bladder; gi glottis; 



" /id., hepatic duct; t.n., internal nostril; 



tractions disappear and reappear int., small intestine; Ig., lung; l.i., large 



at alternate levels they cause •"'^f'^^:'"- ''^■^'■■' "^Z' '""''"'"'^ 



teeth; ovd., opening of oviduct; p., pan- 

 a very thorough mixing of the creas; p.d., pancreatic duct; pyl., pyloric 



intestinal contents. Food in the sphincter; sp., spleen; st., stomach; 



t., tongue; ur., opening of ureter; v.t., 

 small intestine comes in contact vomerine teeth. (Redrawn with modi- 



with three digestive juices: bile, ^^^^t'^^^ ^'""'- ^°Tc^, "u'^Z °^ -^"^ 



^ •' . ' otomy, copyright, 1902, by Macmillan 



which comes from the Uver by and Co., Ltd., reprinted by permission.) 



way of the bile duct; pancreatic 



juice, entering from the pancreas through the pancreatic duct ; and 



intestinal juice, from glands in the Uning of the duodenal region 



