COMPOSITION OF HUMAN SALIVA. 173 



Longet states, furthermore, that he has examined the sa- 

 liva from a great number of persons, under all conditions, 

 and has never failed to demonstrate the presence of the sul- 

 pho-cyanide. Its proportion he found very variable, and in 

 some cases it was so slight that the reaction with the per- 

 chloride of iron did not immediately manifest itself; but by 

 slowly evaporating the liquid to one-half or one-third of its 

 original volume, the reaction became manifest in all cases. 1 



In examining the saliva of a number of persons, Bernard 

 found some in which no red color was produced by the addi- 

 tion of the perchloride of iron, and he remarked that all in 

 which the reaction was manifested were in the habit of 

 smoking. This led him to add a little nicotine to the speci- 

 mens of saliva which did not present this reaction, when a 

 red color, somewhat less intense than in the other specimens, 

 was produced. 2 If, in these experiments, the saliva had been 

 slightly evaporated, it is probable that the reaction would 

 have been manifested. We have frequently demonstrated 

 to a medical class the presence of a sulpho-cyanide in the 

 saliva of persons who had never used tobacco. 



It is probable that the sulpho-cyanide of potassium is a 

 constant ingredient of each of the three varieties of saliva. 

 It has been found in the parotid, in cases of salivary fistula, 

 and was noted by Dalton in the saliva taken from the duct 

 of Steno, though in this case the saliva contained an organic 

 principle which interfered with the test, but which could 

 be precipitated by alcohol and separated by filtration. 3 

 I^onget found the sulpho-cyanide in the saliva from the sub- 



1 Longet found the perchloride of iron a much more delicate test than the 

 persulphate, which is sometimes used. When the peculiar reaction shows itself 

 after evaporating the liquid, it is not due to mere concentration, but to some 

 change which occurs during the process ; for the color may be obtained when the 

 quantity of water .lost by evaporation has been restored. (BERNARD, Lemons de 

 Physiologic Experimentale, Paris, 1856, tome ii., p. 140.) 



2 BERNARD, Liquides de VOrganisme, Paris, 1859, tome ii., p. 244. 



3 See p. 157 (note). The analysis of Mr. Perkins gives the sulpho-cyanide of 

 sodium instead of the sulpho-cyanide of potassium. 



