434 PHYSIOLOGICAL CHEMISTRY. 



Lymph is a clear, colorless, or slightly yellow liquid of a faint 

 alkaline reaction ; in composition it closely resembles chyle, but 

 differs from it in containing smaller quantities of fibrin and fatty 

 matters. 



Saliva is secreted by several glands situated in the mouth, and 

 represents in its mixed condition a viscid, generally slightly alkaline, 

 tasteless, inodorous liquid of a specific gravity of 1.002 to 1.008. It 

 contains of 



Water 99U9 per cent. 



Ptyalin 0.12 " 



Epithelium and mucin 0.13 " 



Fatty matters 0.11 " 



Salts 0.15 



Ptyalin, the active principle of saliva, is a ferment which has the 

 power of converting starch into maltose and small quantities of 

 dextrose. Intermediary between the starch and sugar are two 

 products known as erythrodextrin and achroodextrin. Starch is recog- 

 nized by a deep blue color produced by a solution of iodine and 

 potassium iodide in water. Erythrodextrin gives a mahogany 

 brown or violet color, and achroodextrin, maltose or dextrose do not 

 color the iodine solution at all. The composition of ptyalin is 

 doubtful. Among the various salts of saliva is found potassium 

 sulphocyanate, as may be shown by the addition of a drop of ferric 

 chloride solution, which produces a deep red color, disappearing on 

 the addition of mercuric chloride (difference from meconic acid). 



Experiment 65. To a few c.c. of thin starch paste add an equal volume of 

 saliva, mix well and digest at a temperature of 35-40 C. (95-104 F.) for 

 about half an hour. Examine the liquid for sugar by Fehling's solution. 



Gastric juice is a liquid secreted by the follicles of the stomach. 

 It can be obtained, in a fairly normal condition, either from animals 

 (dogs) or from man, by the aid either of gastric fistulse, or' of the 

 stomach-pump. It is a thin, nearly colorless liquid, having a some- 

 what sour taste, an acid reaction, and a specific gravity varying from 

 1.004 to 1.010. The total solids are generally less than 1 per cent., 

 nearly one-half being inorganic salts, chiefly the chlorides and phos- 

 phates of alkali and alkaline earth metals. The organic matter 

 present, and amounting to about 0.3 per cent., is chiefly pepsin and a 

 little mucin. 



Organic acids, chiefly lactic and butyric, are frequently found in 



