24 HUMAN BIOLOGY 



keep food from spoiling, we need only to bring about con- 

 ditions that are unfavorable for th^ growth of microor- 

 ganisms. 



For instance, everybody knows that meat, milk, and eggs 

 must be put on ice in summer if they are to be kept for any 

 length of time. Indeed, many food materials of this sort will 

 remain in a more or less fresh condition for months or even 

 years if they are in cold storage. It has been proved, how- 

 ever, that food products kept in cold storage for a long time 

 are often unsafe for human consumption. On the other 

 hand, we demonstrated (17, A) that a high degree of heat will 

 kill bacteria, and so meats* that have been cooked and milk 

 that has been Pasteurized or scalded will keep longer than 

 they do when left uncooked. If meats, vegetables, or fruits 

 are heated to the boiling point in cans and sealed up at 

 once, they may be permanently prevented from spoiling. 



Ham and herring are often smoked to preserve them, 

 while pork and codfish are soaked in a strong solution of 

 salt (brine) to keep them from the decaying action of bacteria. 

 Another method of preserving' food is by depriving it of 

 water. Dried beef, apples, hay, and seeds will keep indefi- 

 nitely if no moisture is allowed to get to them. Previous 

 to the passage of the Pure Food Law by Congress in 1906, 

 many unscrupulous dealers were accustomed to use borax, 

 formaldehyde, 1 and other chemicals to prevent their food 

 supplies from spoiling. Fortunately for the health of the 

 consumer, this method of food preservation has been largely 

 stopped by the enforcement of the law to which we have 

 just referred. 



1 Method of determining whether or not formalin has been added 

 to milk. Into each. of two test tubes or flasks put an equal quantity of 

 fresh milk. To one of the glasses add a drop or two of formaldehyde 

 solution. Then to each add a volume of hydrochloric acid equal to 



