THE TRANSFORMATION OF FOOD 37 



slightly opalescent fluid, familiar to every one as 

 saliva. The granular substance in the gland cells 

 is known as zymogen, or the enzyme-producer, the 

 enzyme itself is termed ptyalin. If we make a very 

 dilute starch mucilage by adding a few grains of 

 starch to a wine-glassful of warm water and pour 

 into this some saliva, keeping the whole at a tem- 

 perature about that of the human body (i.e., 100F.), 

 a gradual change takes place in the starch as the 

 result of the action of the ptyalin upon it. If a few 

 drops of a solution of iodine be added to a sample of 

 the original starch mucilage, the mucilage takes on 

 an indigo-blue colour, but no such colouration 

 results from the addition of iodine to the sample 

 which has been acted on for a considerable time by 

 saliva. On the other hand, with the aid of another 

 re-agent known as Fehling's solution (a mixture of 

 Rochelle salts, copper sulphate and caustic soda in 

 certain proportions) we can demonstrate the presence 

 of a new substance, malt sugar, which, unlike starch, 

 is soluble in water. The enzyme has effected the 

 alteration of the starch into malt sugar, and one 

 remarkable feature in the process is that the enzyme 

 is not used up nor destroyed during the transformation. 

 Further, a comparison of the chemical formulae of 

 starcli and malt sugar shows that the enzyme has 

 made the starch take up a molecule of water. Thus 

 2 (C,.H 1() 0.) starcli becomes C^H^O,, malt sugar 

 by the addition of H 2 water. Similar results 

 may be obtained by preparing an extract of ger- 

 minating barley, and causing it to act on starch. 

 The ferment, which acts in the same way as ptyalin, 

 in this case goes by the name of diastase. 



Let us now attempt to gain some general 

 idea of the nature of the alimentary canal of 



