RELATION OF RATE TO PERCENTAGE COMPOSITION. 499 



He l showed, further, that in parotid saliva, obtained by stimulating 

 Jacobson's nerve, there is similarly a decrease in the percentage of solids 

 as the secretion goes on, and, no doubt, it is a general rule for all 

 salivary glands. 



KELATION OF THE KATE OF SECRETION TO THE PERCENTAGE 

 COMPOSITION OF SALIVA. 



Heidenhain 2 investigated the relations existing between the rate of 

 secretion and the percentage composition of saliva. He showed that an 

 increase in the rate of secretion was accompanied by an increase in the 

 percentage of salts, and this whether the gland had secreted for a long 

 time or for a short time. 



An example of this is given in the following experiment, in which the 

 chorda tympani was stimulated with currents of varying strength, and a few 

 c.c. of saliva collected in each case. The samples of saliva are arranged in the 

 table in the order of their rate of secretion : 



Order of sample 



Mean rate of secretion 



per min. in c.c. . 

 Percentage of salts . 



15 

 34 



18 

 29 



19 

 25 



22 

 32 



1-6 

 37 



2-0 



58 



2-2 



44 



2-5 

 57 



3'2 



58 



It will be noticed that the percentage of salts does not quite go hand 

 in hand with the rate of secretion. But it is almost impossible to keep 

 the rate of secretion constant during the time of collecting a sample of 

 saliva, and to this the divergences may, in the main, be attributed. 



A closer relation between the rate of flow and the percentage of saliva was 

 observed by Werther, 3 and by Langley and Fletcher. 4 Heidenhain found the 

 percentage of salts to have an upper limit, with increased rate of secretion. 

 This he gave as *5 to '6 per cent., though in one case '66 per cent, was found. 

 Becher and Ludwig had earlier found in one case '78 per cent. Werther, and 

 Langley and Fletcher found the maximum percentage to be *77. From the 

 observations of the latter, it appears that the faster the rate of secretion, the 

 less increase there is in the percentage of salts for a given increase in rate of 

 secretion. This is indicated in the following table : 



1 Heidenhain, Arch. f. d. gcs. PhysioL, Bonn, 1878, Bd. xvii. S. 23. During eleven 

 hours' stimulation the percentage of solids sank from 0'88 per cent, to 0'49 per cent. 



2 Ibid., Bd. xvii. p. 1. Earlier observations on the same lines were given by him in 

 1868 in his " Studien." 



3 Arch. f. d. ges. PhysioL, Bonn, 1886, Bd. xxxviii. S. 293. 



4 Phil. Trans., London, 1889, p. 109. 



