BODY TISSUES AKD FLUIDS 475 



that salivary digestion may proceed for a considerable period after the 

 food reaches the stomach, owing to the slowness with which the food 

 contents are mixed with the acid gastric juice. Ptyalin acts best in a 

 neutral or faintly acid medium, (combined acid) ; but is readily destroyed 

 by a trace of free hydrochloric acid. It acts more efficiently when some- 

 what diluted. 



It has been shown by Chittenden and Smith that the diastatic action 

 of human saliva can be taken as a definite measure of the amount of 

 ferment present, only when the saliva in the digestion mixture is diluted 

 at least 50 or 100 times. They have found that the limit of dilution at 

 which decisive diastat : c action manifests itself with formation of reduc- 

 ing bodies is 1 to 2000 or 3000. Myers and Dellenbaugh, working with a 

 very delicate method, have recently observed that when 0.01 c.c. of normal 

 human saliva is allowed to act on 10 mg. of soluble starch in a volume of 

 2 c.c. for 30 minutes at 40 C., 30 to 45 per cent of the starch is con- 

 verted to sugar when the diluent is water and 46 to 50 per cent when 

 the diluent of the saliva is 0.3 per cent sodium chlorid. The Cl ion has 

 long been recognized to have a pronounced facilitating action. Essentially 

 the same range of figures were found in such pathological conditions as 

 diabetes, nephritis and gastric ulcer. A few individuals were encoun- 

 tered, however, who for periods showed low activities, figures 10 to 20, 

 that were not readily explained, although it may be noted that they 

 complained of gastric distress. Representatives of different nationalities 

 were found to vary within the same normal limits, which opposes the 

 view advocated by some of the adaptation of. salivary secretion to diet. 

 As shown by Chittenden and Richards, saliva secreted after a period of 

 glandular activity, as before breakfast, manifests greater amylolytic power 

 than the secretion obtained after eating. Corresponding with this in- 

 crease in amylolytic power occurs an increase in the proportion of alkaline- 

 reacting salts, but the increased amylolysis is due primarily to an increase 

 in the amount of active enzyme contained in the saliva. 



Marshall has suggested that the ratio between the mathematical ex- 

 pressions for the total neutralizing power of normal resting saliva and 

 normal activated saliva from a. given individual is a "salivary factor" 

 the magnitude of which appears to be indicative of immunity from caries 

 or the reverse. Shepard and Gies were unable to substantiate this claim. 



The thiocyanate content of human saliva has been the topic of a 

 number of studies. The saliva of smokers has been shown to have a much 

 higher content of potassium thiocyanate than that of nonsmokers. Schnei- 

 der found that the average content for six. smokers was 0.013 per cent, 

 while for ten ngjismokers it was 0.003 per cent. Sullivan and Dawson 

 have studied the thiocyanate content of the saliva in pellagra. With 

 active symptoms the thiocyanate content is lower than later when the 

 characteristic symptoms have disappeared. The thiocyanate content of 



