Relation of Ptyalin Concentration to the Diet. 53 



orthodox Hindus, but we were not able to secure this material. 

 The experiment has, however, been carried out in nature on a 

 large scale in the case of the herbivora. 



1 . Carnivora. — There is no ptyalin in the saliva of the dog, 

 the cat and the fox (6 individuals). The slight diastatic power of 

 the saliva of these animals is due to traces of blood and lymph 

 diastases. 



2. Herbivora. — The diastatic power of the parotid and mixed 

 saliva of monkeys (7 individuals) is the same or less than that of 

 man. The ptyalin concentration in the rabbit's parotid saliva is 

 the same or slightly greater than that of man. But the parotid 

 and mixed saliva of the goat (6 individuals) and the horse ( 1 3 

 individuals) has no diastatic power. 



3. Thus, while the absence of ptyalin in the saliva of many 

 (probably all) carnivora and its presence in rodents and primates 

 may suggest adaptation, the absence of it in some herbivora nulli- 

 fies such a conclusion. The saliva of monkeys ought on the 

 adaption hypothesis to have greater ptyalin concentration than 

 that of man. But we do not wish to be understood as holding 

 that the ptyalin producing processes have been evolved without 

 any relation to the nature of the food, because we must have data 

 from all the mammalian groups before we are in position to deter- 

 mine whether the absence of ptyalin signifies atrophy or incipient 

 evolution. 



II. The relation of ptyalin concentration to the rate of secretion 

 of the saliva. 



1. Weak acids (acetic) in the mouth are a more efficient stim- 

 ulus to the secretion of the parotid than mechanical stimuli (dry 

 sand, crackers, flour, cotton) and within limits the stronger the 

 acid the greater the rate of secretion. The concentration of the 

 human parotid saliva varies directly with the rate of secretion, just 

 as is the case of lower mammals. 



2. The concentration of the ptyalin in the parotid saliva of the 

 rabbit varies directly with that of the organic solids in the case of 

 gland anemia and on stimulation of the cervical sympathetic nerve 

 (Carlson and Ryan). Since in the rested gland the organic solids 

 increase with the rate of secretion we would expect the rapidly 

 secreted parotid saliva to contain more ptyalin than the slowly 



