CHEMICAL CONSTITUENTS OF BODY AND FOOD. 29 



and ferments by yeast. Maltose has the same properties as glucose, 

 but is distinguished in two ways: (1) the light-rotating power of 

 glucose is 56 degrees, while maltose is 150 degrees; (2) the reducing 

 of metallic salts by glucose is equal to 100, while that of maltose is 

 but 66. The sugar in blood is a glucose. 



By moistening barley and germinating it in heaps at a constant 

 temperature, the starch of the barley is converted into dextrose and 

 maltose. This change is brought about by the ferment called dias- 

 tase, which is found in barley. This product, when dried, is denom- 

 inated -malt, which, when it is acted upon by yeast, produces the 

 malted beverages, beer and ale. Maltose by invertin of yeast is 

 changed into glucose. 



Amyloses, or Polysaccharides. Under the influence of dilute 

 mineral acids the amyloses are changed by boiling or are transformed 

 into glucose. Starch presents a polarizing cross: black cross upon 

 a white ground or a white cross upon a black ground. Starch does 

 not reduce copper solution nor is it fermentable by yeast. When 

 iodine is added to starch it gives a blue color. 



Glycogen, or animal starch, does not reduce copper salts nor is 

 it fermentable by yeast. During the hydrolysis of starch dextrin is 

 formed as an intermediate product. Dextrins colored red by iodine 

 are called erythrodextrins ; those not colored by iodine are called 

 achroodextrins. 



2. FATS. 



Fats form a more or less variable proportion of the animal 

 economy. They come to us principally in the form of animal food. 

 but to some extent in vegetable food, also, especially in seeds, nuts, 

 fruit, and roots. 



The fats contain in their substances a fatty principle having 

 acid properties a sort of fatty acid. When acted upon by alkalies 

 and ferments, this acid becomes separated and a sweet principle 

 known as glycerin makes its appearance. Thus fats may be said to 

 be compounds of fatty acids with glycerin. It would seem, however, 

 that the glycerin had not pre-existed in the fats, as the united weight 

 of the glycerin and the fatty acid produced exceeds that of the fat 

 originally employed. 



In bone-marrow, adipose tissue, and milk, the fats are very 

 prominent components. The adipose tissue consists of nucleated 

 vesicles filled with fatty matter. The vesicles are closely packed 

 together and are surrounded by a network of blood-vessels which 



