26 APPLIED BACTERIOLOGY 



The Bacillus prodigiosus failed to grow after being frozen 

 for fifty-one days, as did also the Proteus vulgaris. The 

 Staphylococcus pyogenes aureus withstood freezing for sixty- 

 five days, and the typhoid bacillus for 103 days. Sub- 

 cultures made at intervals showed, however, a diminution 

 in number of the bacteria. A similar diminution in 

 number would perhaps have occurred in old cultures in 

 which the material for growth was exhausted, independent 

 of freezing; for the bacteria, like the higher organisms, 

 die in time as the result of degenerative changes in the 

 protoplasm of the cells, and continued vitality in a culture 

 depends on continued reproduction. 



Eepeated freezing and thawing was found by Prudden to 

 be more destructive to the typhoid bacillus than continuous 

 freezing. Cadeac and Malet kept portions of a tuberculous 

 lung in a frozen condition for four months, and found that 

 at the end of this time tuberculosis was produced in guinea- 

 pigs by injecting a small quantity of the material. 



(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. Loftier 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 



