PRESERVATION OF FOOD PRODUCTS FROM BACTERIA. 319 



It is only necessary to refer to the fact that many other sub- 

 stances are used for the preservation of food which are more 

 powerful in their action and distinctly deleterious. The use of 

 salicylic acid, of borax, of boracic acid, of formalin (under 

 various commercial names) is only too common. These pre- 

 servatives must one and all be condemned as deleterious to 

 health. It is quite illegitimate to use them in the preservation 

 of food products. 



PRESERVATION BY HERMET1CAL SEALING. 



One of the most important methods of preserving perishable 

 food products was invented a century ago, long before the 

 significance of bacteria was known, and long before the mean- 

 ing of the process was understood. It was invented by 

 Appert, and consisted in first destroying by heat all of 

 the bacteria present in the material to be preserved, and 

 subsequently sealing it hermetically so as to prevent the 

 access of more bacteria. It was at first supposed that the 

 significance of the sealing was to prevent the access of air, but 

 it is now known that its purpose is simply to prevent the 

 entrance of bacteria ; for if these can be kept out, the presence 

 of air does not interfere with the preservation. It is interest- 

 ing to note that this method of preservation of food products 

 was invented and put to a wide practical use, while scientists 

 were disputing and laboriously experimenting over the prob- 

 lem of spontaneous generation. The experiments by which 

 scientists tried to settle this question consisted in exactly the 

 same devices as just mentioned, viz., the heating of various 

 organic materials to a high temperature to kill all living organ- 

 isms and then, after sealing hermetically, watching to see if 

 more life developed in the sterilized mass. While the scientists 

 were disputing as to the results, the method of canning was 

 put into practical use, and every can of preserved fruit was 

 evidence against spontaneous generation. 



