MEDICAL METHODS 499 



methods employpd in the preservation of foods are devices 

 employed to prevent the action of bacteria upon food 

 stuffs. 



Relation of business methods to bacteria. — In the para- 

 graphs on the action of bacteria as a living cell we noted 

 certain conditions which were favorable to their develop- 

 ment, and vice versa. The methods used in the preserva- 

 tion of food depend upon a proper use of the facts there 

 noted. For example, in cold storage methods we have the 

 application of the principle that bacteria are rendered in- 

 active by cold. Foods, therefore, will not decay so long as 

 they are kept sufficiently cold to secure this inactivity. We 

 also noted that bacteria need water to develop in. Dried 

 meats, therefore, and foods preserved in salt or sugar, either 

 are free from this necessary water or have the water re- 

 placed by solutions of salt or sugar, which are not favor- 

 able to the action of the plants. The packing of foods in 

 air-tight cans which have been submitted to temperatures 

 of boiling water meets two conditions unfavorable to bac- 

 teria. The heating of the food and can kills the germs that 

 might be present, while the sealing prevents the bacteria 

 in the air from entering after the foods are cooled. Certain 

 chemicals also kill bacteria, and it has been customary in 

 the past to make use of some of these as preservatives of 

 food. This latter method should always be carefully in- 

 spected, since often the chemicals used may be in such 

 quantity and of such a nature as to be themselves dan- 

 gerous to health. The pure food law in some of its clauses 

 covers just this ground. 



Medical methods. — The human body is extremely well 

 protected from disease-causing bacteria, since the only ave- 

 nue of approach to most of its organs is through the blood; 



