736 POPULAR SCIENCE MONTHLY. 



the cholera spirillum is destroyed by ten minutes' exposure to a 

 temperature of 52 C. ; the typhoid bacillus by 56 ; the micrococ- 

 cus of pneumonia by 52 ; the streptococcus of erysipelas (S. pyo- 

 genes) by 54 ; etc. According to Loeffler, the bacillus of glanders 

 is destroyed in ten minutes by a temperature of 55 C. ; the bacil- 

 lus of diphtheria by 00. The experiments of Yersin 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 any of the patho- 

 genic bacteria mentioned would be speedily disinfected by immer- 

 sion in water heated to 70 C. or above, and water or milk recently 

 heated to the same temperature would evidently be without dan- 

 ger so far as infection by these "disease germs" is concerned. 

 The recommendation 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 knowledge that 

 organic liquids can be sterilized by heat constitutes the founda- 

 tion upon which the bacteriology of the present day has been 

 established. To obtain reliable information with reference to the 

 biological characters of any particular micro-organism it is neces- 

 sary to experiment with pure cultures, and this requires a sterile 

 culture medium. 



It is hardly necessary to call attention to the fact that an im- 

 mense industry in the preservation of food products depends upon 

 the sterilization of these products by heat, and their preservation 

 in hermetically sealed receptacles. 



When Pasteur demonstrated the fact that sterile organic 

 liquids, when protected by a sterilized cotton air- filter, can be 

 kept indefinitely without undergoing any putrefactive or fermen- 

 tative 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 particu- 

 lar species of low organisms. Thus the alcoholic fermentation of 

 a saccharine liquid was found to be due to a torula (Torula cere- 

 visicE), the acetic fermentation of an alcoholic liquid to a bac- 

 terial ferment (Pasteur's Mycoderma aceti], etc. Subsequent re- 

 searches show that alcoholic fermentation may be induced by 

 several species of torula, and even by certain bacteria ; while the 

 number of bacterial ferments now known to science is very con- 

 siderable and is constantly being added to. Among the most im- 

 portant of these we may mention the Bacillus acidi lactici, which 

 is the usual cause of the acid fermentation of milk ; the various 

 anaerobic bacilli which give rise to the formation of butyric acid 

 in solutions containing starch, dextrin, sugar, or salts of lactic 

 acid; the bacteria which cause the alkaline fermentation of 



