1835.] Human Saliva. 377 



the largest gland, and the other five glands yield more than 

 six times the quantity of fluid secreted by it. 



With regard to the effect of different kinds of food in 

 increasing the quantity of saliva, Mitscherlich found great 

 difficulty in experimenting with precision, but every one 

 knows the disparity between soft and hard bodies in pro- 

 ducing saliva. Mitscherlich estimates the effect of the 

 former to the latter as 3 to 5. 



Chemical nature of Saliva. — The saliva in the mouth acts 

 upon tests very variously, being generally slightly acid, often 

 neutral, and sometimes alkaline. The cause seems to be 

 that the saliva remains in contact with the mucus, which is 

 separated from the mucus glands in the mouth. The saliva 

 from the fistula which was exempt from the mixture was 

 alkaline during mastication, and acid at other periods. 

 Twice, however, shortly before eating, the saliva was found 

 to be slightly alkaline, and immediately after eating it was 

 perceived to be still alkaline, but remained so only for a 

 short time. When the saliva was drawn into the mouth 

 by the exertion of the patient it was observed to be slightly 

 acid. In this case the saliva from the fistula was neutral, 

 or scarcely acid. The saliva in the mouth often indicated 

 a free acid, and in the instance where the saliva from the 

 fistula was acid, the saliva of the mouth was completely 

 neutral. Mitscherlich was inclined to attribute this to the 

 chemical combination of the saliva with the mucus, by 

 which ammonia was extracted. 



During eating and drinking the saliva was invariably 

 alkaline, for after the first mouthful the acid disappeared, 

 and reddened litmus paper became blue. # 



Specific gravity. — Tiedemann and Gmelin found the 

 density of saliva produced during the smoking of tobacco 

 1*0043. In Mitscherlich's experiments it varied from 

 1*0061 to 1-0088, but when collected during the usual 

 hospital dinner, its specific gravity was almost constant at 

 1-0074. He found also, that the specific gravity was 

 greater, in proportion to the cessation from eating. 



The density of the saliva in the trials of Tidemann and 



* These statements are at variance with those of Dr. Donne, (Ann. de Chim. 

 lvii. 402.) who affirms, that the saliva is always alkaline in the healthy state, but 

 that he has found it possessing an acid re-action in diseases of the stomach, espe- 

 cially in gastritis. — Edit. 



