THE VITAL CONDITIONS OF BACTERIA. 95 



tended experiments of the authors just mentioned 

 put their duration of life at from one to five hours 

 according to the mode of desiccation (the results are 

 similar to those of R. Koch in his first experiments). 

 But it is evident from the results obtained by all 

 writers that desiccation experiments must be espe- 

 cially varied and many-sided, if they are to be con- 

 vincing. The surprising result has recently been 

 obtained in regard to very many varieties which are 

 sensitive to desiccation (this is true particularly of 

 the cholera vibriones) that, under certain circum- 

 stances, they may remain alive, when dried, for a 

 much longer time. Thus Koch found the duration 

 of life to be a few hours; Kitasato (Z. H., V., 135) 

 fourteen days; French writers and Berckholz (A. G. 

 A., V., 1) found it one hundred and fifty to two hun- 

 dred days under specially favorable conditions. Ac- 

 cording to most writers these favorable conditions in- 

 clude: stay in the desiccator, removal from agar or 

 potato cultures instead of bouillon cultures, the use 

 of silk threads instead of pieces of glass. Special 

 mention must also be made of the fact that in none 

 of these experiments could anything of the nature of 

 spores (arthrospores) be positively recognized. 



5. RELATIONS TO OXYGEN AND SOME OTEHR GASES. 



In their relations to oxygen bacteria are divided 

 usually into three classes (Fliigge and Liborius) : 



/. Strict Aerobics. Growth occurs only when the 

 air finds access; any obstruction to the latter inter- 

 feres with the growth. Free oxygen is particularly 

 necessary to the development of spores. 



