POWER AND COMPOSITION OF HUMAN SALIVA. 257 



clearly that human mixed saliva does fluctuate in amylolytic 

 power throughout the twenty-four hours, and further that the 

 starch-digesting power of the saliva secreted before breakfast, 

 for example, is greater than that of the secretion collected 

 after breakfast. Our results afford distinct confirmation of 

 the general truth of this observation. Hofbauer states in his 

 paper that the only previous work bearing upon this subject 

 is that by Chittenden and Ely.* The latter work, however, 

 has no bearing whatever upon the question of possible varia- 

 tion in the amylolytic power of the secretion at different 

 periods of the day. Indeed, hi the paper in question it is 

 distinctly stated that " the saliva was collected generally an 

 hour or two after breakfast," with the distinct object of avoid- 

 ing possible variations in composition due to the period of 

 collection. The sole object of that investigation was to 

 ascertain whether there is any connection between possible 

 variations of alkalinity and the amylolytic power of saliva. 

 The results there reported afford no indication whatever of the 

 relative amylolytic action of the secretion for different periods 

 of the day, since the fluids studied were invariably collected 

 at essentially the same hour. It was ascertained, however, 

 that the alkalinity of mixed saliva as measured by titration 

 with a standard acid, using cochineal as an indicator, was 

 fairly constant for a given individual at a given period of the 

 day (9-10 A.M.), while saliva from different individuals may 

 show a constant difference in alkalinity, although in the ma- 

 jority of cases the alkalinity varied only within narrow limits. 

 In amylolytic action, however, there were no corresponding 

 differences ; fluctuations were observed, but within too narrow 

 limits to indicate any tangible relation between the two 

 factors. 



It has become the custom to assume that the alkalinity of 

 saliva, as indicated by its reaction toward litmus paper, is due 

 more or less to the presence of sodium carbonate. Thus, in 

 the latest textbook of physiology the statement f is made 



* Chittenden and Ely, Amer. Chem. Journ., 1883, iv, p. 329. 

 t Text-book of Physiology, edited by E. A. Schafer, 1898, i, p. 504. 



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