DIGESTION. 



over it (<>nc grain of starch to one hundred centimetres of 

 water), or by boiling it in :i flask or large test-tube, and then 

 allowing it to cool. Filter the saliva to be used, and distribute 

 it in three test-tubes, introducing into the first, starch mucilage 

 a l, m >_into the second, saliva and into the third, saliva with 

 about three times its hulk of starch paste. Mix them well 



ier by agitation. Then put all three for a few minutes 

 water-batb at 40 C., or warm them gently over a spirit- 

 lamp. Add to each of them liquor potassa> in excess, and a 

 drop or two of solution of cupric sulphate. In the first and 

 second, a light blue precipitate will be thrown down, and the 

 liquid will 'remain colorless; but in the third, the precipitate 

 ill l.e redissolved. and give a blue solution. If 



the liquids are boiled, the precipitate in the first tube, 

 containing starch paste, alone will be blackened, but the liquid 

 will remain colorless. In the second, containing saliva, the 

 precipitate will be partly dissolved, and give to the fluid a 

 color, due to albumin in the saliva, 12. In the third, 

 a yellow or orange precipitate will be formed. This reaction, 

 which is known as T milliner's test, shows that there is no 

 siiiiar either in the saliva or starch used, but that it is formed 

 by the action of the one on the other. Rapidity of conversion 



</</, int<> sugar. Bidder and Schmidt erroneously con- 

 sidered that the conversion of starch into sugar was almost 

 instantaneous. To illustrate this view, introduce saliva into a 

 small Leaker. Place it in a water-bath at 40 C., and when it 

 U warmed through, let a little dilute starch mucilage, colored 

 with iodine, fall into it drop by drop. As each drop falls it 

 becomes decolorized. The disappearance of the blue color is 

 not dependent on the conversion of starch into sugar, but on 

 the conversion of the iodine into hydriodic acid. Other or- 

 ganic fluids, such as the urine of dogs, according to Schiff, ex- 

 hibit the same react ion. which is probably due to their con- 

 taining deoxidizing substances, for the same effect is produced 

 by Milphurous acid or morphia, both of which absorb oxygen 

 readily. This may be shown by putting starch mucilage 

 colored with a little iodine into a test-tube and diluting it till 

 it forms a clear blue transparent solution. If it is now placed 

 in the warm bath at 40 C., it will remain unaltered, but will 

 at once lose its color on the addition of either of the reducing 



nts above mentioned. 



* 78. Effect of Temperature on the Diastatic Action 

 of Saliva. Take four test-tubes, and carefully introduce a 

 little saliva into each with a pipette. Put the first into a mix- 

 ture of >no\v or ice and salt, the second into a test-tube rack 

 on the table, the third into a water-bath at 40 0.; boil the 

 fourth briskly for two or three minutes, and then allow it to 

 cool. Then add starch paste to each of them, and allow them 



