164 ELEMENTARY PHYSIOLOGY. [XV. 



a. Add iodine ; no colouration is produced (there 

 may be a little tint from dextrin since in 

 mixing the drops a faint colour may escape 

 notice which in a larger quantity of fluid is 

 obvious). 



b. Add an excess of sodium hydrate and a drop 

 of 1 p.c. cupric sulphate and boil ; the fluid 

 turns yellow and a yellow precipitate will be 

 formed showing the presence of sugar. 



9. Boil a little saliva, add it to starch in a test-tube 

 and warm. In half-an-hour divide into two 

 parts and test as in 8 a, b. The blue colour 

 from starch will be as distinct as at first, no trace 

 of sugar will be found; hence boiling destroys 

 the ferment (ptyalin) which converts starch into 

 sugar. 



10. If the saliva used in 8 converts starch into 

 sugar very rapidly dilute it still further for the 

 following experiment. Into each of three test- 

 tubes pour equal quantities of saliva and starch. 

 Place A in a water bath at about 37 C., leave B 

 at the temperature of the room (noting it) and 

 place C in a vessel with ice (it is best to cool 

 the starch and saliva before mixing them). At 

 short intervals take with a glass rod drops from 

 each and add them to drops of iodine on a 

 porcelain plate and so compare the rate of dis- 

 appearance of starch (cp. 8) in the three 

 mixtures. It will disappear much more quickly 

 in A than in B ; in C there will be very little 

 change. 



