HYGIENIC ASPECTS OF NUTKITION 359 



depends upon the kinds of materials from which the protein, 

 fats, and carbohydrates are secured, and upon such factors 

 as the condition of the body and nature of exercise, that 

 statements of definite quantities cannot be considered as 

 an entirely trustworthy guide. It is highly important to 

 make certain that the day's diet includes foods from the 

 various sources vegetables, fruits, and milk, as well as meat 

 and bread. 



It is true, however, that the amounts of food needed may 

 vary greatly according to personal habits, the kind of work 

 in which one is engaged, and the climate. Men engaged in 

 hard physical work in cold climates demand larger quanti- 

 ties of food than here given and a larger proportion of fats, 

 while people in tropical regions may work better with smaller 

 amounts of fats and more carbohydrates. In the same way, 

 the quantity of water needed varies in different climates and 

 with different occupations. 



366. Contaminated food. Nearly all kinds of food may be- 

 come the growing place for bacteria or other organisms that 

 will, if allowed to continue to grow, finally bring about the 

 decay of the food. A review of what was said on this point 

 in connection with the discussion of the bacteria and molds 

 (Chapter VIII) will prove helpful. Sometimes these decay- 

 producing organisms are dangerous to human health and 

 sometimes they are not. For example, the blue molds that 

 grow in Roquefort cheese, or the bacteria that ripen other 

 kinds of cheese, are not unwholesome and, indeed, are the 

 causes of the desired flavors of the different kinds of cheese. 



Preservatives are sometimes used to prevent the decay of 

 foods. Small amounts of formalin, benzoate of soda, or other 

 chemicals may be put into the liquid foods as milk, and will 

 prevent decay; but while from superficial examination such 

 foods may appear to be good, they may at the same time 

 contain enough of the preservative to prove injurious. When 

 milk under exposure to the temperature of ordinary air 



