68 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



The submaxillary saliva comes next (2-1 to 2*5 per cent.). When 

 artificially obtained by stimulation of nerves in the dog the saliva 

 obtained by stimulation of the sympathetic is richer in solids than 

 that obtained by stimulation of the chorda tympani. The parotid 

 saliva is poorest in total solids (0'3 to 0'5 per cent.), and contains no 

 mucin. Mixed saliva contains in man an average of about 0'5 per- 

 cent, of solids : it is alkaline in reaction, due to the salts in it ; and 

 has a specific gravity of 1002 to 1006. 



The solid constituents dissolved in saliva may be classified 

 thus : 



( a. Mucin : this may be precipitated by acetic acid. 

 anic b. Ptyalin : an amylolytic ferment. 



I c. Protein : of the nature of a globulin. 



V d. Potassium sulphocyanide. 



/ e. Sodium chloride : the most abundant salt. 



Inorganic ' f' ^ tner sa l* s : sodium carbonate ; calcium phosphate 

 and carbonate ; magnesium phosphate ; potassium 

 chloride. 



THE ACTION OF SALIVA 



The action of saliva is twofold, physical and chemical. 



The physical use of saliva consists in moistening the mucous 

 membrane of the mouth, assisting the solution of soluble substances 

 in the food, and in virtue of its mucin lubricating the bolus of food 

 to facilitate swallowing. 



The chemical action of saliva is due to its active principle, 

 ptyalin. This substance belongs to the class of unorganised ferments 

 or enzymes, and to that special class of unorganised ferments which 

 are called amylolytic (starch-splitting) or diastatic (resembling 

 diastase, the similar ferment in germinating barley and other grains). 



The starch is first split into dextrin and maltose ; the dextrin is 

 subsequently converted into maltose also : this occurs more quickly 

 with erythro-dextrin, which gives a red colour with iodine, than with 

 the other variety of dextrin called achroo-dextrin, which gives no 

 colour with iodine. Brown and Morris give the following equa- 

 tion :* 



10(C 6 H 10 5 ) W + 4wH 2 



[starch] . [water] 



=4nC 12 H 22 O u + (0 6 H 10 5 ) B + (C 6 H 10 6 ) M 



[maltose] [achroo-dextrin] [erythro-dextrin] 



Ptyalin acts in a similar way, but more slowly on glycogen : it 



