THE SALIVARY GLANDS. 761 



Composition of the Secretion. The saliva as it is found in the 

 mouth is a colorless or opalescent, turbid, and viscid liquid of 

 weakly alkaline reaction to litmus paper, and a specific gravity of 

 about 1.003. It may contain numerous flat cells derived from the 

 epithelium of the mouth, and the peculiar spherical cells known as 

 salivary corpuscles, which seem to be altered leucocytes. The 

 important constituents of the secretion are mucin, a diastatic en- 

 zyme known as ptyalin, maltase, traces of protein and of potassium 

 sulphocyanid, and inorganic salts, such as potassium and sodium 

 chlorid, potassium sulphate, sodium carbonate, and calcium car- 

 bonate and phosphate. The carbonates are particularly abundant 

 in the saliva, and the secretion in addition contains much carbon 

 dioxid in solution. Thus, Pfliiger found that 65 volumes per cent, 

 of CO 2 might be obtained from the saliva, of which 42.5 per cent, 

 was in the form of carbonates. The amount of CO 2 in solution 

 and combined is an indication of the active chemical changes 

 occurring in the gland. 



Of the organic constituents of the saliva the protein exists in 

 small and variable quantities, and its exact nature is not determined. 

 The mucin gives to the saliva its ropy, mucilaginous character. 

 This substance belongs to the group of combined proteins, glyco- 

 proteins (see Appendix), consisting of a protein combined with a 

 carbohydrate group. The most interesting constituent of the mixed 

 saliva is the ptyalin or salivary diastase. This body belongs to the 

 group of enzymes or unorganized ferments, whose general properties 

 have been described. In some animals (dog) ptyalin seems to be 

 normally absent from the fresh saliva. 



The secretions of the parotid and the submaxillary glands can be 

 obtained separately by inserting a cannula into the openings of the 

 ducts in the mouth, or, according to the method of Pawlow, by trans- 

 ferring the end of the duct so that it opens upon the 'skin instead of 

 in the mouth, making thus a salivary fistula. The secretion of the 

 sublingual can only be obtained in sufficient quantities for analysis 

 from the lower animals. Examination of the separate secretions 

 shows that the main difference lies in the fact that the parotid saliva 

 contains no mucin, while that of the submaxillary and especially of 

 the sublingual gland is rich in mucin. The parotid saliva of man 

 seems to be particularly rich in ptyalin as compared with that of the 

 submaxillary. 



The Secretory Nerves. The existence of secretory nerves to the 

 salivary glands was discovered by Ludwig in 1851. The discovery is 

 particularly interesting in that it marks the beginning of our knowl- 

 edge of this kind of nerve fiber. Ludwig found that stimulation of 

 the chorda tympani nerve causes a flow of saliva from the submaxil- 

 lary gland. He established also several important facts with regard 



