DIGESTION 



429 



live mechanism may be, it somcLimes tails, ami the acidity, mechanical 

 irritation, action of pepsin, or possibly all three lead to gastric (or 

 peptic) ulcers. In the context of this problem it is interesting to note 

 that pepsin has some hydrolytic action on itself. Such autohydrolysis 

 partially degrades the molecule and liberates peptides in the process. 

 Pepsin does not attack the peptide bonds between all possible com- 

 binations of amino acids. Rather it is primarily concerned in the 

 hydrolysis of only those bonds connecting the aromatic amino acids 

 tyrosine, phenylalanine, and tryptophan with other amino acids, thus 

 accounting for the incompleteness of the equilibrium hydrolysis of 

 proteins. 



Ruminants 



Animals related to cattle, sheep, and goats possess a compound 

 stomach of four sections known as (1) the rumen or paunch, (2) the 

 reticulum or honeycomb, (3) the omasum, and (4) tlT,e abomasum or 

 true stomach, corresponding closely to the single-sac stomach of other 

 mammals. As shown in Figure 17-2 the first two regions are not 

 actually separate compartments; the reticulum is really a lobe of the 

 rumen. Furthermore the omasum is closely associated physiologically, 

 so that rumen, reticulum, and omasum combined form a large fer- 

 mentation vat. Anatomically these chambers are regarded as enlarge- 

 ments of the esophagus. 



As a rule the ruminant masticates its food very imperfectly at the 



Dorsal sac 



Posterior 

 blind sacs 



Ventral sac-^'^ 

 Pylorus 



Rumen 



Oesophagus 



Reticulum 



Omasum 



Abomasum 



FIGURE 17-2. Ruminant stomach. Right view with rumen raised. (Courtesy of W. B. 



Saunders Co.) 



