32 HUMAN PHYSIOLOGY. 



Upon meat the gastric juice has a decidedly disintegrating action. The 

 connective tissue is first dissolved, the fibres are separated, the sarcolemma 

 softened, and the whole reduced to a grumous, pultaceous mass. Milk 

 undergoes coagulation in from ten to fifteen minutes, the casein being 

 precipitated in the form of soft flocculi, which are easy of transformation 

 into peptone. Upon Vegetable tissues, the gastric juice exerts also a dis- 

 integrating action; the cellulose and woody fibres are dissolved and the 

 nutritive principles liberated. Bread undergoes liquefaction quite readily. 



The Principal Action of the gastric juice, however, is to transform the 

 different albuminous principles of the food into peptones or albuminose, the 

 different stages of which are due to the acid and pepsin respectively. When 

 freed from its combination, the hydrochloric acid converts the albumin 

 into acid albtimin or parapcptone ; while this intermediate product is being 

 formed, the pepsin converts it at once into peptone. In order that the 

 digestion of albumin may be complete, it is necessary that both the acid 

 and pepsin be present in proper quantity. Before digestion, the albuminous 

 principles are insoluble in water and incapable of being absorbed. After 

 digestion, they become soluble and are readily absorbed. Peptones differ 

 from the albumins in being 



1. Diffusible ', passing rapidly through the mucous membrane and walls 

 of the blood vessels. 



2. Non-coagulable by heat, nitric or acetic acids; but are readily precipi- 

 tated by tannic acid. 



3. Soluble in water and saline solutions. 



4. Assimilable by the blood ; when injected into it, they do not reappear 

 in the urine. 



Gastric juice exerts no influence either upon grape sugar, cane sugar, 

 starch or fat. 



Gastric Digestion occupies on the average from 3 to 5 hours, but 

 varies in duration according to the nature and quantity of the food, exercise, 

 temperature, etc. 



The Amount of gastric juice secreted in 24 hours varies, under normal 

 conditions, from 8 to 14 pounds. 



Movements of the Stomach. As soon as digestion commences, the 

 cardiac and pyloric orifices are closed ; the walls of the stomach contract 

 upon the food, and a peristaltic action begins, which carries the food along 

 the greater and lesser curvatures, and thoroughly incorporates it with the 

 gastric juice. As soon as any portion of the food is digested, it passes 

 through the pylorus into the intestine. 



