528 THE POTATO 



of different ages and account in some measure for 

 the flavor of potatoes. 



"If peeled potatoes are exposed to the air the 

 outer surface turns brown, just as does the flesh 

 of many fruits. Such change is due to the action 

 of enzyms or unorganized ferments naturally 

 present in the plants. In the presence of the oxy- 

 gen of the air they work upon tannin-like bodies in 

 the tuber or fruit in such a way that the latter 

 change color. In the case of potatoes this brown- 

 ing may be prevented by putting the peeled tubers 

 into salted water or even into cold plain water. 



"In the condition in which they are purchased 

 potatoes resemble such succulent carbohydrate 

 foods as turnips and beets, with an average water 

 content of 90 per cent., more than they do such dry 

 carbohydrate foods as flour or rice with an average 

 of 12 per cent. The condition in which foods are 

 eaten should also be taken into account, for if the 

 value of a food is judged solely by its chemical 

 composition as it is found in the market a wrong 

 impression may be obtained. For instance, po- 

 tatoes as purchased consist of one fifth and rice 

 of seven eighths nutritive material. The first 

 inference is that rice is more than four times as 

 nutritious as potatoes. In one sense this is true 

 that is to say, a pound of uncooked rice contains 

 more than four times as much nutritive material 

 as a pound of raw potatoes. But if we take about 

 four pounds of potatoes that is, the amount nec- 

 essary to furnish as much nutritive material as the 

 pound of rice the composition and nutritive 

 value of the two quantities will be just about the 

 same, while from a pecuniary standpoint the 

 advantage would be on the side of the potatoes. 

 The chief difference in the two foods before cook- 



