26 APPLIED BACTERIOLOGY 



(4) Desiccation. — Cultures of various micro-organisms, 

 when kept moist, retain their vitality for a considerable 

 time, but this varies with the different species. Sternberg 

 found cultures of B. typhosus, B. prodigiosus, and others to 

 be alive after being hermetically sealed for eighteen months. 

 Some species die quickly, but most of them retain their 

 vitality for months. The cholera spirillum (' comma ' 

 bacillus) will remain alive for months if kept moist ; but 

 Koch and Kitasato found that a broth culture, dried in the 

 form of a very thin film, was incapable of development after 

 three hours' drying. Pfuhl found the typhoid bacillus, dried 

 under the same conditions, to retain its vitality for eight 

 to ten weeks. Loffier found that the diphtheria bacillus 

 resists desiccation for four or five months. Cadeac and 

 Malet produced tuberculosis in guinea-pigs by injecting 

 material from the lung of a tuberculous cow which had 

 been kept in the form of a desiccated powder for five months, 

 but at a later date the virulence was lost. 



(5) Action of Electricity. — Many workers have made ex- 

 periments to determine the action of electrical currents on 

 various bacteria, but the results hitherto obtained are very 

 indefinite and discordant. It is possible, however, that in 

 the future this agent, the application of which increases 

 daily, may play an important part in the destruction of 

 bacteria. 



(6) Action of Chemical Agents. — Chemical agents are de- 

 structive to bacteria by virtue of their poisonous action on 

 protoplasm. The haloid elements, mineral acids, alkalies, 

 metallic salts, and various organic compounds, all exert a 

 strong germicidal or retarding action on the growth and 

 development of micro-organisms. 



The Antagonism of Micro-organisms. — The mutual an- 

 tagonism or influence of growth of one species upon the 

 growth of another has been specially studied by Freuden- 



