Bauhaus-Universität Weimar

Handbook for the Physiological Laboratory. Text
Burdon-Sanderson, John Scott E. Klein Michael Foster T. Lauder Brunton
minutes. Take a part of the fluid from each, and test it for sugar, 
either by Trommer’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 body. Now place the first 
and fourth test-tubes in the water-bath at 40° C., allo w them to re¬ 
main 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 totally destroyed by 
* 79. Influence of Acids and Alkalies on the Diastatic 
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 065 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 potassæ 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, care¬ 
fully 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 mouth, but is swallowed unchanged, it is important 
for us to know whether the transformation 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 secre¬ 
tion, 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 drops of liquor potassæ, and to the other a few drops of 
a solution of potassium carbonate, mix a little starch mucilage with


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