BY DR. LAUDER BRUNTON. 461 



to remain where they arc for five or ten minutes. Take a part 

 of the fluid from each, and test it for sugar, either by Trom- 

 mer's or Moore's tests. (See 155.) None will be found in 

 the first or fourth, a little in the second, and more in the third. 

 Thus we learn that saliva does not act, or acts very slowly, at 

 the freezing point, that it acts at the temperature of the air, and 

 still more quickly at the temperature of the bod}'. Now place 

 the first and fourth test-tubes in the water-bath at 40 C., allow 

 them to remain for several minutes, and test again for sugar. 

 It will be found in the first but not in the fourth. This shows 

 that the power of saliva to transform starch into sugar, is 

 merely suspended by exposure to a very low temperature, but 

 is totalty destroyed by boiling. 



* 79. Influence of Acids and Alkalies on the Dias- 

 tatic Action of Saliva. Dilute acids do not arrest the 

 action of saliva upon starch ; stronger acids do so for a time, 

 but when they are neutralized the action again goes on. 



Take three test-tubes, and put into each equal parts of 

 saliva and starch paste. Add to the first its own bulk of 

 water, to the second a similar proportion of distilled water, 

 containing 0.65 per cent, of commercial hydrochloric acid, and 

 to the third the same quantity of dilute acid of 10 per cent., 

 and keep them for five minutes at 40 C. Add liquor potassse 

 to the first and second, and test for sugar. It will be found 

 in nearly equal quantity in both. Take part of the fluid in 

 the third tube, and test it for sugar. None will be found. 

 Neutralize the remainder with carbonate of potash, carefully 

 avoiding excess, and replace the test-tube in the water-bath 

 for a little while. On again testing it, sugar will be found to 

 be present As the greater part of the starch we eat is not 

 transformed into sugar in the moiuh, but is swallowed un- 

 changed, it is important for us to know whether the trans- 

 formation goes on in the stomach or whether it is arrested by 

 the acid gastric juice. The strength of the dilute acid just 

 employed (0.2 of real hydrochloric acid) is nearly the same 

 as that of the gastric juice, and the experiment shows that in 

 the healthy stomach the conversion of starch into sugar may 

 go on rapidly. In some pathological conditions the acidity 

 of the gastric juice is abnormally increased, and the action of 

 the saliva may be suspended so long as the food remains in 

 the stomach, but when the acid is neutralized by the intestinal 

 secretion, the action will go on again. 



Alkalies. Caustic potash and soda, when added to the 

 saliva in excess, put a stop to its action on starch, and its 

 diastatic power is not restored by neutralization. Its action 

 is suspended by sodium and potassium carbonates, ammonia 

 and lime-water, but restored by neutralization. Put saliva in 

 two test-tubes and add to one several drop's of liquor potassa3, 



