292 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



of ptyalin on starch. It will be found, however, that hydrochloric acid 

 does not appear in the gastric juice of the horse until the latter stages 

 of gastric digestion, the acidity in the early stages being due to the 

 presence of lactic acid. It has further been proved that lactic acid , 

 even when present in 2 or 3 per cent., will not arrest the conversion of 

 starch by the saliva. Therefore in the horse starch may still be con- 

 verted in the stomach into sugar. In the ruminant animal all the starch 

 is probably converted into sugar in the rumen, where the reaction is 

 alkaline, and here also, therefore, the acidity of the gastric juice does not 

 interfere with the digestion of starch, even though it may not take place 

 in the stomach, whatever starch escapes the saliva being acted on by 

 the pancreatic juice. In carnivora, where the gastric juice is highly 

 acid, starchy matters seldom enter into the composition of their food, 

 while in the omnivora, man especially, the saliva possesses a higher 

 diastatic power than in other animals ; therefore the conversion of starch 

 in the mouth will be much more rapid, and even though suspended in the 

 stomach, is again resumed in the small intestine under the action of the 

 pancreatic juice. So, also, when the amount of sugar formed reaches 

 from 1^ to 2£ per cent., saccharification is arrested, but will be renewed 

 when the fluid is diluted. The transformation of boiled starch mucilage 

 is very much more rapid than that of raw starch. This is clue to the 

 fact that it is only the granulose of the starch granules which is con- 

 verted into sugar. In the raw starch granules the granulose is contained 

 in an unyielding cellulose envelope, and is not accessible to the salivary 

 ferment. When starch is boiled the cellulose envelopes are ruptured; 

 the granulose then passes parti y into solution, and is then readily acted 

 on by the saliva. 



The diastatic action of the saliva of different animals varies very con- 

 siderably. In almost all it is less active than- in man, with the possible 

 exception of the saliva of the herbivora. The latter appears to be more 

 active on raw starch than that of the carnivorous animals. Thus, it has 

 been found that the saliva of the horse will convert crushed raw starch into 

 sugar in one-quarter of an hour, and it has been proved experimentally 

 that in the horse the conversion of raw starch into sugar, through the 

 action of the saliva, takes place in the stomach. It is worthy of note 

 that the individual salivary secretions of the horse appear to possess 

 this amylolytic power to a less degree than the mixed saliva. It has 

 been, however, found that, in addition to acting on starch, the saliva of 

 the horse is also capable of converting cane sugar into grape sugar. 

 The saliva of the horse is further inactive on the cellulose of hay. 



Examination of the substances escaping from an oesophageal fistula 

 in the horse fed on starchy food shows that practically no conversion 

 of starch into sugar occurs in the mouth. This, indeed, would be ex- 



