FOOD AND DIGESTION 59 



peptones appear. First the protein swells up and 

 changes into an acid albumin called syntonin, which 

 passes through two successive stages primary and sec- 

 ondary proteoses before peptone is produced. 



Rennin is the ferment which changes milk to clabber. 

 It acts well in the presence of hydrochloric acid. Cow's 

 milk forms a solid mass, or firm clot, not unlike the clot 

 of blood save in color, which squeezes out the wliey af- 

 ter standing. Human milk forms a loose flocculent clot, 

 probably more easily mixed with gastric juice. Rennin 

 does not digest the casein, which is digested by pepsin 

 as are other proteins. The clotting is probably to pre- 

 vent the immediate passage of milk into the duodenum 

 before stomach digestion could begin. There seems to 

 be no other food substance on which rennin acts. 



The stomach has no power of digesting starchy foods 

 which leave it in the condition in which mouth digestion 

 has left them. Fats are not appreciably acted upon by 

 the gastric ferment, but are more or less liquefied and 

 mixed with the other foods in the chyme. By soaking 

 into and around particles of bread or other food, fats 

 may interfere with stomach digestion. 



Stomach digestion is more preparatory than complete. 

 Apparently about half of the proteins pass into the 

 duodenum as either peptones or proteoses, 20 per cent as 

 unchanged proteins while but a small part of the re- 

 mainder is absorbed from the stomach. Some native 

 proteins are not acted on by the pancreatic juice and 

 must receive preparatory treatment in the stomach. 

 Mixing the foods, warming them, separating the fats 

 from other foods with which they are mechanically 

 mixed, emulsifying them, partly digesting protein and 

 regulating the amount poured into the duodenum seem 

 the chief functions of the stomach. 



