1(> Messrs. J. N. Langley and H. M. Fletcher. [Nov. 15, 



chance of winning truth. To me at least it appears that the line of 

 thought flows in a true channel, that it may help to give a meaning 

 to the observations of the spectroscopist, and that many interesting: 

 problems, here barely alluded to, may perhaps be solved with sufficient 

 completeness to throw light on the evolution of nebulas and planetary 

 systems. 



III. "On the Secretion of Saliva, chiefly on the Secretion of 

 Salts in it." By J. N. LANGLEY, M.A., F.R.S., Fellow of 

 Trinity College, and H. M. FLETCHER, B.A., Trinity College, 

 Cambridge. Received August 17, 1888. 



(Abstracb.) 



Heidenhain has shown that when saliva is obtained by stimulating 

 the chorda tympaui, the percentage of salts in the saliva depends upon 

 the rate o secretion, so that the faster the secretion the higher the 

 percentage of salts is up to a limit of about O6 per cent. Werther has 

 come to the same conclusion, but finds that the percentage of salts 

 may be as much as 0'77. Both in Heidenhain's and in Werther's ex- 

 periments there are many exceptions to this rule, attributed by them 

 to variations in the rate of secretion of saliva during the time of 

 collecting any one sample. 



We have repeated, with some modifications, the experiments of 

 Heidenhain, paying especial attention to the rate of secretion of saliva, 

 and find in 10 out of 11 cases, that his law of an increase in the per. 

 centage of salts with an increase in the rate of secretion holds. 

 The single exception may be due to a modification of the blood-flow 

 through the gland during the time of collecting the saliva. The 

 slowly secreted saliva contains a low percentage of salts, whether it is 

 produced by a weak nerve stimulus, or by a very strong nerve 

 stimulus which lowers the irritability of the nerve-fibres. 



We do not find any rate of secretion, beyond which an increase in 

 rate fails to increase the percentage of salts in the saliva. The incre- 

 ment in the percentage of salts decreases, however, with each equal 

 successive increment in the rate of secretion. 



As a rule in saliva obtained by injecting pilocarpin, the percentage 

 of salts follows Heidenhain's law ; we take the exceptions to be due to 

 the action of pilocarpin upon the circulation, the blood-flow through 

 the gland being less than normally accompanies the degree of stimula- 

 tion of the gland cells. 



The percentage of salts in saliva obtained by stimulating the sym- 

 pathetic is higher than corresponds to its rate of secretion, the saliva 

 obtained by stimulating the chorda being taken as a basis of com- 

 parison ; this sympathetic saliva may be secreted at y^th of the rate 



