THE JUICES POURED OUT UPON THE FOOD. 65 



ordinary mixed human saliva is true also of the saliva ob- 

 tained from the dog after stimulation of the chorda tympani 

 nerve or after poisoning with curare. 1 



Among the inorganic constituents of the saliva are the 

 chlorides, carbonates, bicarbonates, phosphates, and sul- 

 phates of sodium, potassium, magnesium, and calcium. The 

 escape of carbon dioxide from the saliva on standing allows 

 the precipitation of the bicarbonate of calcium as the car- 

 bonate. This substance is the chief constituent of salivary 

 calculi and " tartar." 



Much importance was at one time attached to the quanti- 

 tative determination of the sulphocyanate in the saliva as 

 an indicator of the rate of protein metabolism, for it is gener- 

 ally believed that this substance is a product of protein me- 

 tabolism. MOORE, however, believes that its estimation is of 

 ifttle value. 



The gases of the saliva are oxygen, nitrogen, and carbon 

 dioxide. The latter predominates, and is found chiefly in 

 chemical combination. 



Among the organic constituents of the saliva the ferments 

 amylase and maltase are of the greatest importance. The 

 former of these two is characterized by its action upon starches 

 which are under its influence converted into maltose. Mal- 

 tase is especially effective in causing a still further cleavage 

 of this sugar into dextrose. While food is being chewed, 

 therefore, and for some time after it reaches the stomach, the 

 starches contained in it are undergoing a change which con- 

 verts them into substances readily absorbed by the alimentary 

 tract. The rnucin contained in the saliva is probably of 

 little more than mechanical use in supplying food with a 

 coating which allows the more ready passage into and 

 through the oesophagus. 



The oesophagus itself is studded with small mucous glands 

 which secrete a small amount of a ropy fluid rich in mucin. 



1 See MUNK: Centralblatt fur Physiologic, 1902, XVI, p. 33, 



