5 



THE SALIVAR Y GLANDS. 



The experiments on the parotid gland given by Heidenhain show a 

 general but not a very close relation between the rate of secretion and the 

 percentage of salts in the saliva. 



Sodium chloride forms the larger part of the salts in saliva. The 

 percentage both of this and of sodium carbonate varies directly with the 

 rate of secretion. 1 The salts insoluble in water, the chief of which is 

 calcium carbonate, do not seem to follow this rule, or at any rate only 

 partially, for, whilst there is sometimes an increase in the percentage 

 of insoluble salts, with increased rate of secretion, this is by no means 

 always the case; 1 they appear to decrease in amount during the 

 progress of the secretion, as if in part they arose from a store in the 

 gland itself. 



The following experiment from Werther will illustrate the variations in 

 the percentage of different salts. The saliva was obtained from a dog by 

 stimulating the chorda tympani : 



The relation thus determined between the percentage of salts and 

 the rate of secretion, holds for chorda saliva and for pilocarpine saliva 2 

 secreted under normal conditions. But it is not a universal rule. Thus, 

 sympathetic saliva has a much higher percentage of salts than corre- 

 sponds to its rate of secretion, if chorda saliva be taken as a standard of 

 comparison. And the rule does not hold for chorda or pilocarpine saliva, 

 when the blood flow through the gland is much diminished, or when 

 the character of the blood is much altered. On this I shall say more 

 presently. 



Heidenhain also showed that in a fresh gland an increase in the rate 

 of secretion is accompanied by an increase in the percentage of organic 

 substance in the saliva. In the experiment given below, for example, 

 an increase in the rate of flow of the submaxillary saliva of the dog, 

 from 0'14 c.c. to 0'87 c.c. in one minute, was accompanied by an increase 

 from O52 to 1/54 in the percentage of organic substance. But when 

 a certain amount of the stored-up substance of the gland cells has been 

 secreted, an increase in rate of secretion no longer leads to an increase 

 in the percentage of organic substance in the saliva secreted in a 

 given time. 



The closeness of the relation between percentage of organic sub- 

 stance and rate of secretion from a fresh gland seems to me to have 

 been much exaggerated. No doubt there is a relation of the kind, but, 

 in actual experiments, it is frequently overridden by other factors. 

 1 Werther, op. cit. 2 Langlcy and Fletcher, op. cit., supra. 



