120 THE AMERICAN MONTHLY [April 



55° C; the bacillus of diphtheria by 60°. The experi- 

 ments of Yersiii show that the tubercle bacillus does not 

 survive exposure for ten minutes to a temperature of 70° 

 C. The practical value of such knowledge is apparent. 

 Articles of clothing infected with many of the patho- 

 genic bacteria mentioned would be speedily disinfected 

 by immersion in water heated to 70° C or above and 

 water or milk recently heated to the same temperature 

 would evidently be without danger so far as infection by 

 these "disease germs" is concerned. The reconxmenda- 

 tion of sanitarians that water or milk or food suspected 

 of being contaminated by pathogenic bacteria should be 

 exposed to a boiling temperature before it is used is based 

 upon the experimental data referred to; and the know- 

 ledge that organic liquids can be sterilized by heat con- 

 stitutes the foundation upon which the bacteriology of 

 the present day has been established. To obtain relia- 

 ble information with reference to the biological charac- 

 ters of any particular micro-organism it is necessary to 

 experiment with pure cultures, and this requires a 

 sterile culture medium. 



It is hardly necessary to call attention to the fact that 

 an immense industry in the preservation of food pro- 

 ducts depends upon the sterilization of these products by 

 heat, and their preservation in hermetically sealed re- 

 ceptacles. 



When Pasteur demonstrated the fact that sterile or- 

 ganic liquids, when protected by a sterilized cotton air 

 filter, can be kept indefinitely without undergoing any 

 putrefactive or fermentative change, he also proved that 

 such changes are due to the presence of micro-organisms; 

 and, extending his investigations, he found that certain 

 definite kinds of change are due to particular species of 

 low organisms. Thus the alcoholic fermentation of a 

 saccharine liquid was found to be due to a torula [Torula 

 cei'evisiw), the acetic fermentation of an alcoholic liquid 



