DIGESTION 313 



into fatty acids and glycerol if they are in a very tine state of 

 subdivision, as in milk, but it has no action on fats not so 

 subdivided. It is probable that this lipase comes from 

 the duodenum. AVhen fats are contained in the protoplasm 

 of cells, they are set free by the digestion of the protein 

 covering. 



On Carbohydrates the free mineral acid of the gastric juice 

 has a slight action at the body temperature, splitting the 

 polysaccharids and disaccharids into monosaccharids. 



(4) Digestion of the Stomach Wall. — Wlien the wall of the 

 stomach dies either in whole, as after the death of the animal, 

 or in part, as when an artery is occluded or ligatured, the 

 dead part is digested by the gastric juice and the wall of the 

 stomach may be perforated. The typical gastric ulcer which 

 so frequently occurs in man in anaemia is of this nature. In 

 the normal condition, a substance may be extracted from 

 the mucous membrane which antaijonises the action of 

 pepsin and may be called antipepsin. 



(5) Antiseptic Action of the Gastric Juice. — In virtue of 

 the presence of free HCl, the gastric juice has a marked 

 action in inhibiting the growth of, or in killing, bacteria. 

 Some organisms, while they do not multiply in the stomach, 

 pass on alive to the intestine, where they may again become 

 active. 



(6) Influence of Various Diets upon the Gastric Secretion. — 

 This has been chieHy investigated by Pavlov on dogs with a 

 gastric pouch (p. 309). 



He found that — (1) The amount of secretion depends 

 upon the amount of food taken. (2) The amount and the 

 course of secretion vary with the kind of food taken. Thus, 

 with flesh the secretion reaches its maximum at the end of 

 one hour, persists for an hour and then rapidly falls, while 

 with bread it reaches its maximum at the end of one hour, 

 rapidly falls, but persists for a much longer period than in 

 the case of flesh. (3) The digestive activity of the secretions 

 was tested by allowing them to act upon ca})illary glass tubes 

 filled with egg-white coagulated by heating (Mett's tubes). The 

 extent to which this was digested out of the tube in unit of 

 time gave the activity of the secretion. It varies with the 



