522 DIGESTION 



and is known as whey ajbumose. From studies on molecular weight it 

 is believed that the paracasein is produced from casein by the splitting 

 of the molecule of the latter into two, from which it would appear that 

 the action of this enzyme is nothing more than the first stage in the 

 hydrolysis of the casein molecule. The whey albumose, according to this 

 view, is a by-product. 



There are many investigators, however, who believe that rennin and pepsin are not 

 identical, since an infusion of the stomach of a calf has a powerful clotting action 

 on milk but a very weak digestive one on egg white, whereas a similar infusion from 

 the stomach of a pig shows exactly the reverse properties. This question is one of so 

 controversial a nature that it would be out of place to go into it further here. It 

 should be pointed out, however, that, when the gastric contents are acid in reaction, 

 milk will become clotted by the action of the acid itself quite independently of any 

 pepsin or rennin the juice may contain. This acid clotting of milk is probably of a 

 different chemical nature from that produced by the enzymes. 



On other foodstuffs than proteins the action of the gastric juice is 

 relatively unimportant, although polysaccharides may be considerably 

 broken down in the cardiac end of the stomach on account of the action 

 of swallowed saliva (see page 489), and disaccharides, as we have seen, 

 may become split by the hydrolyzing effect of the hydrogen ion. Fat 

 digestion also takes place in the stomach when the fat is taken in an 

 emulsified condition, as in milk and egg yolk, but not when in masses, 

 as in meat or butter. This action is due to the presence of a fat-splitting 

 enzyme, or lipase, in the gastric juice. 



