SALIVA. 385 



Saliva freed from these flocks is quite transparent, often colour- 

 less, but sometimes it acquires a yellowish hue. At least a phial 

 of saliva which I have kept for 25 years has assumed a rather 

 deep brownish yellow colour, but still retains its transparency. 



Alcohol added to saliva occasions a white precipitate. On 

 heating the liquid this precipitate is partly redissolved ; but it 

 falls down again when the liquid cools. 



Nitrate of silver throws down a precipitate easily soluble in 

 ammonia. 



Tincture of nut-galls throws down a light brown precipitate, 

 soluble by heat, but again appearing when the liquid cools. 



Acetate of lead throws down a copious white precipitate, not 

 soluble by heat, but disappearing on the addition of acetic acid. 



Sulphuric acid gives a slight flocky precipitate. 



Caustic potash or ammonia produces no sensible effect. 



Treviranus first observed that saliva got a red colour when a 

 little perchloride of iron was mixed with it. Tiedemann and 

 Gmelin have inferred that this colour is produced by a minute 

 quantity of sulphocyanic acid contained in saliva. With me the 

 experiment does not succeed ; but I have been told by Dr Al- 

 exander Stewart, that the saliva of smokers was found to strike 

 a red with perchloride of iron. Would it not seem from this as 

 if the sulphocyanic acid in saliva were generated by the action 

 of tobacco smoke ? 



Such are the effects of reagents upon saliva. Let us now see 

 what are its constituents. 



Mitcherlich evaporated 66.775* parts of saliva, of specific gra- 

 vity 1 -0083, to dryness in vacuo over sulphuric acid. The resi- 

 due weighed 1*08 parts, or 1*617 per cent. It was divided by 

 means of water and alcohol into the four following portions : 



1. Insoluble in water and in alcohol of 0.863, 0-281 



2. Soluble in water, but not in alcohol of 0-863, 0-352 



3. Soluble in water, but not in alcohol of 0-800, 0'296 



4. Soluble in water, and in alcohol of 0*800, 0-192 



1-121 

 Excess, . 041 



1-080 

 * The quantity was 66'775 grammes, or almost exactly 1030 grains* 



B b 



