The Animal Body. 



221 



When the food reaches the fourth stomach, it meets with the 

 characteristic secretion of that organ, the gastric juice. This 

 juice is secreted by glands located in the mucus membrane of 

 the stomach. It is a watery fluid, containing various salts, as 

 chlorides and phosphates of calcium, magnesium, sodium and 

 potassium, free hydrochloric acid and the two enzymes, pepsin 

 and rennin. The combination of pepsin and the acid is the ef- 



On the left stomach of the horse. A, end of the oesophagus; B, pyloric 

 end, or beginning of the intestine. On the right stomach of the 

 sheep. O, oesophagus; P, rumen; R, reticulum; F, omasum; 

 C, abomasum; I, commencement of the small intestine; 1, oesophagal 

 groove; 2, opening between omasum and abomasum. 



fective agent in the digestion. They are secreted by different 

 gland cells in the stomach walls and the amount of hydrochloric 

 acid secreted during 24 hours by a normal man, under ordinary 

 conditions of diet, amounts to what would constitute a fatal dose 

 of acid, if taken at one time in concentrated form. The main 

 action of gastric juice is exerted on the proteins of the food, 

 which under its influence, are gradually dissolved and converted 

 into soluble products, known as proteoses and peptones. This 

 enzyme, like the ptyalin of the saliva, is influenced by tern- 



