THE SALIVA. 113 



amounts on stimulation of these fibres than of the corresponding 

 cerebral fibres. According to Levene, the submaxillary mucin con- 

 tains the chondroitin-sulphuric acid complex, or a closely allied 

 group. 



To the presence of the mucin the viscid, stringy character of the 

 saliva is due. The substance can be obtained by precipitation with 

 acetic acid, and it is to be noted that, in contradistinction to the 

 mac in-like substances which belong to the class of the nucleo-albu- 

 mins, the precipitated mucin is insoluble in an excess of the acid. 

 In dilute solutions of the alkalies it is soluble, and it is thus 

 possible by repeated precipitation and solution to obtain the mucin 

 in fairly pure form. In alcohol and water it is insoluble, although 

 in the latter it swells to form a jelly-like material. Unlike the 

 albumins, it is not coagulated by heat ; but, like these, it gives the 

 xanthoproteic reaction, the biuret reaction, and Millon's reaction. 

 It contains also a small amount of sulphur. On boiling with dilute 

 mineral acids mucin is decomposed into a substance which resembles 

 acid albumin, and into a carbohydrate-like body which reduces 

 Fehling's solution. This has been regarded as identical with Land- 

 wehr's animal gum ; Hammarsten, however, states that from the 

 mucin of the submaxillary gland a gum-like substance is obtained 

 which contains nitrogen. On decomposition with strong mineral 

 acids mucin yields leucin, tyrosin, and laBvulinic acid (see also page 

 45). In the dry state it occurs as a white or yellowish-gray 

 powder. 



Within the cells mucin exists as so-called mucinogen, which prob- 

 ably represents a compound of mucin with an additional albuminous 

 substance. 



Sulphocyanides. Traces of sodium sulphocyanide are in man 

 usually found in every specimen of normal saliva. It is secreted 

 by all the salivary glands, but in largest amount by the parotids. 

 In other animals its presence is not so constant, and in some indeed 

 it is not found. In man also it is at times absent. 



To demonstrate the presence of sulphocyanides, it usually suffices 

 to treat a few cubic centimeters of saliva, which have been slightly 

 acidified with hydrochloric acid, with a few drops of a very dilute 

 solution of perchloride of iron, when a red color will be seen to 

 develop. If no result is obtained in this manner, a larger quantity, 

 such as 100 c.c. is evaporated to a small volume and tested as 

 described. 



Nitrites. Small amounts of nitrites may also at times be 

 observed, and are no doubt derived from the nitrates ingested. To 

 test for these, about 10 c.c. of saliva are treated with a few drops 

 of Ilasvay's reagent, and heated to a temperature of 80 C., when 

 in the presence of nitrites a red color develops. 



Ilasvay's reagent is prepared as follows : 0.5 gramme of sulph- 

 anilic acid in 150 c.c. of dilute acetic acid is treated with 0.1 

 gramme of naphtylamin, and dissolved in 20 c.c. of boiling water. 



