158 DIGESTION. 



The following facts with regard to the properties of the 

 parotid saliva observed "by Dalton are given in his own 

 words, in a communication kindly made in answer to certain 

 inquiries : 



" On the 28th of July, 1863, I obtained, from a strong, 

 healthy man, about two drachms of the mixed saliva of the 

 mouth, by causing him to hold in his mouth for a short time 

 a clear glass stopper, and collecting the secretion as it was 

 discharged. 



" One hour afterward 1 obtained, from the same man, four 

 drachms of pure parotid saliva, by introducing a long silver 

 canula into the natural orifice of Steno's duct, on the left 

 side, and collecting the saliva as it flowed from the outer ex- 

 tremity of the canula. 



" The two kinds of saliva compared as follows : 



" Both were distinctly alkaline in reaction ; the parotid 

 saliva rather the more so. 



" The parotid saliva was rather clear and watery in ap- 

 pearance ; .the saliva of the mouth was quite opaline, with 

 admixture of buccal epithelium, but became clear on filtra- 

 tion. 



" The parotid saliva was rendered turbid by the action of 

 heat, and by the addition of nitric acid, as well as sulphate 

 of soda in excess ; but not by sulphate of magnesia, nor by 

 ferro-cyanide of potassium with acetic acid. 



" The saliva of the mouth, filtered clear, became turbid by 

 heat and by nitric acid ; but showed no precipitate by either 

 sulphate of soda or sulphate of magnesia in excess. There 

 was also a slight precipitate on the addition of pure acetic 

 acid, which did not take place in the parotid saliva. 



" The parotid saliva showed no traces of sulpho-cyanogen 

 on the addition of the perchloride of iron ; but they were 

 distinctly marked in the buccal saliva. 



" On mixing the two kinds of saliva with boiled starch, 

 and keeping the mixture at the temperature of 100 Fahr., 

 sugar was present in loth specimens at the end of five min- 



