466 GRASSES OF IOWA. 



occurring in the saliva of very young children, and also is 

 generally present ia the saliva of other animals, with the pos- 

 sible exception of the dog. 



The time of action of the saliva on tha food varies with the 

 nature of the animal; in man it is quite short, but in other ani- 

 mals such as the cow, the food is pafsed to the first compart- 

 ment of the four-chambered stomach, and when a supply of food 

 has been gathered it is returned to the mouth to be thoroughly 

 ground and crushed by the teeth and well mixed with the 

 saliva. It then passes to the other parts of the stomach for 

 further digestion. In the horse the crushed and ground mass 

 which has been thoroughly mixed with saliva passes to the 

 stomach, where the ptyalin acts for a w^hile and the juices of 

 the stomach are apparently withheld in order that the change 

 of the starch to sugar may continue for a time. 



The ptyalin acts at a temperature slightly above 10-4'' P. 

 Small quantities of free acids will prevent the ptyalin acting 

 on starch. Some salts like magnesium sulphate in very small 

 quantifies accelerate, while larger quantities hinder, the action 

 of the enzyme. 



The glands in the mouth which secrete the saliva are the 

 most active in the animal body, secreting as they do eight to 

 fourteen times their entire mass in saliva. The food, after 

 having been ground and mixed with the saliva, passes to the 

 stomach*. Here it meets with a condition which is entirely 

 different from that in the mouth. In the stomach we fiod a 

 liquid called the gastric juice. It is similar to the saliva in 

 containing a large quantity of water, as may be seen in the 

 following analysis! (parts per 1000): 



Human. Dog. Sheep. 



Water 994.404 973 062 986.143 



Organic substance 3.195 17.127 1.234 



Hydrochloric acid 200 3.050 1.234 



Calcium chloride C61 .624 .114 



Sodium chloride 1.465 2.507 4.369 



Potassium chloride 550 1.125 1.518 



Ammonium chloride .4S6 .473 



Calcium phosphate ) 



Magnesium phosphate r • 125 .226 .577 



Ferric phosphate ) 



♦ The saliva also acto In a mechanical manner, aiding the passage of the food to the 

 stomach, or In other words, as a lubrlcaot. 



t Halleburton, Chem., Fhys. and Path. p. 638. 



