5°° 
THE SALIVARY 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 : — 
Amount 
of Saliva 
obtained 
in c.c. 
Rate of 
Secretion 
per Minute 
in c.C. 
Percentage 
of 
Organic 
Substances. 
Percentage 
of 
Salts. 
Percentage 
of 
Insoluble 
Salts. 
Percentage ! Percentage 
of ' of 
NaCL \.i.COj. 
1 
2 
3 
4 
17-6 
14-2 
16-2 
16-2 
0-176 
0-890 
0-216 
1-0S2 
0-30 
1-12 
0-12 
0-64 
■ 
0-35 
0-43 
0-21 
0-42 
0-019 
0-060 
0-015 
0-030 
0-29 0-042 
0-30 0-067 
0-13 0-029 
0-27 0-046 
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 0T4 c.c. to - 87 c.c. in one minute, was accompanied by an increase 
from - 52 to T54 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. - Langley and Fletcher, op. cit., supra. 
