COMPOSITION OF HUMAN MIXED SALIVA. 259 



gen alkali phosphates, with possibly some alkali bicarbonate. 

 The submaxillary saliva of the dog, however, obtained by 

 stimulation of the chorda tympani is usually, at least, faintly 

 alkaline to phenolphthalein ; * consequently this fluid may owe 

 its alkalinity in part to sodium carbonate. These facts, which 

 admit of easy confirmation, are worthy of some consideration, 

 since they have an important bearing upon the normal con- 

 ditions governing enzyme action. 



I. RELATIVE ALKALINITY AND ACIDITY OP HUMAN 

 SALIVA BEFORE AND AFTER EATING. 



In this series of experiments the saliva was collected from 

 one individual, stimulation of the secretion being effected by 

 chewing a small piece of rubber. About 15 c.c. of fluid were 

 collected each time. The portion collected before breakfast 

 was obtained at 7.30 A. M., half an hour before eating, while 

 the portion collected after eating was obtained fifteen minutes 

 after the close of the meal. The alkalinity was determined by 

 titrating the saliva (5 c.c.) with a decinormal solution of 

 sulphuric acid, using lacmoid as an indicator, while the acidity 

 was determined by the use of a decinormal solution of sodium 

 hydroxide, the indicator being phenolphthalein. The alkalinity 

 was calculated in terms of sodium carbonate, and is also 

 expressed as milligrams of H 2 SO 4 (absolute) required to neu- 

 tralize 1 gram of saliva. The degree of acidity is expressed as 

 milligrams of NaOH (absolute) required to neutralize 1 gram 

 of saliva. Following are the results obtained (see table, p. 260). 



A glance at these results shows that the alkalinity of saliva, 

 as indicated by lacmoid, is noticeably greater in most cases in 

 the fluid secreted after a night's rest, before breakfast, than in 

 the secretion obtained after the glandular activity induced by 

 the morning meal. Before and after dinner, however (1 p. M.), 

 this distinction is less conspicuous. It is also interesting to 

 note that the average alkalinity, expressed in terms of sodium 

 carbonate, is somewhat higher with lacmoid as an indicator 



* Chittenden, Science, n. s., 1897, v, p. 902. Also Chittenden, Mendel, and 

 Jackson, Amer. Jour. Physiol., 1898, i, p. 174. 



