ON THE SECRETION OP SALIVA. 
147 
both contain very nearly a normal percentage of salts, it being, we think, a trifle 
higher than normal in IX. on account of the injection of salts taking place shortly 
before {cf. p. 142). The exceptions to the law are X. and XII. 
Taking the rate of secretion of organic substance in IX. to XII., we have :— 
Table XVI. 
Amount of organic 
substance secreted in 
100 min. 
IX. 
•947‘2 
X. 
1-5394 
XL 
•9891 
XII. 
1-3376 
^.e., the stimulus to the gland, as indicated by the rate of secretion of organic substance, 
was considerably greater in X. and XII. than in IX. and XI. In X., notwithstanding 
the stronger stimulus, less water is secreted than in IX. ; probably, then, during the 
secretion of saliva X. less blood was flowing through the gland. And this is the 
more likely in this instance, for, when successive doses of pilocarpin are injected into 
the blood, they produce less and less increase of the blood flow through the gland. 
But, as we have seen, a decreased flow of blood during an increased stimulus is adequate 
to cause an increase in the percentage of salts. A similar line of argument applies to 
XI. and XII. 
A comparison of IX. and XII. shows that there remains an intimate connection 
between the percentage of salts and the rate of secretion of water, for XII. secreted, 
if the foregoing reasoning is sound, under the influence of a stronger stimulus than 
IX. and with less blood flow, and in consequence, having a higher percentage of salts 
than normal, has nevertheless a considerably lower percentage of salts than IX., 
which is secreted at a rapid rate. 
We may consider here one or two other results bearing on this question. In 
Experiment 7 (X. to XII.), increasing the quantity of pilocarpin given, increases the 
rate of secretion’ of organic substance very much more than it increases the rate 
of secretion of water or of salts. When a fairly large dose of pilocarpin is given 
at the beginning of an experiment, a rapid secretion of saliva takes place and the 
percentage of organic substance in it is high. Subsequent doses produce a less 
and less rapid secretion of saliva; so that, although the percentage of organic sub¬ 
stance remains high, the rate of secretion of organic substance much diminishes. At 
the same time, there is a great decrease in the irritability of the chorda tympani, 
shown by the fact that electrical stimulation of the chorda tympani has very little 
* Langley, ‘Journal of Anat. and Physiol.,’ vol. 11, 1876, p. 176; and ‘Journal of Physiology,’ 
vol. 1, 1878, p. 366. 
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