CH. n] THE CHARACTERS OF BACTERIA 15 



to ferment that carbohydrate. B. typhosus for example after 

 two years' growth in a medium containing lactose acquires the 

 power to ferment this sugar (vide p. 58). 



4. In other cases again the length of the period of cultiva- 

 tion is of less importance than the conditions under which 

 such cultivation takes place. 



(a) Conditions which lower the vitality of a strain may 

 modify its characters. Such conditions include starvation (for 

 example, growth in pure water), acidity of the medium, want 

 of oxygen, the presence of antiseptics, exposure to sunlight, 

 high or low temperatures, symbiosis, etc. 



One example will suffice. A strain of B. ruber of Kiel if 

 heated to a temperature just below that known to kill the 

 organism loses its power to produce pigment (Adami, 1892). 



(b) The crowding together of the organisms on the surface 

 of the medium may lead to a diminution in pigment produc- 

 tion in the staphylococcus aureus (Andrewes and Gordon, 

 1905-6) and an earlier appearance of granular staining forms 

 of the diphtheria bacillus (Denny, 1903). 



(c) The temperature at which organisms grow is respon- 

 sible for certain variations. Laurent (1890) found that 

 a selected strain of B. ruber which had grown for 12 months 

 at a temperature of 25 35 C. without exhibiting a trace of 

 colouration, yielded its characteristic pigment when the tem- 

 perature was lowered to 18 C. An apparent staphylococcus 

 "albus" growing at 37 C. may become a vivid "aureus" at 

 22 C. (Andrewes and Gordon, 1905-6). 



The virulence of B. anthracis is greatly modified by growth 

 at 43 C. and that of B. diphtheriae may be destroyed by 

 subjection to a similar temperature (Hewlett and Knight, 

 1897). 



Wilson (1910) describes an atypical B. typhosus which 

 fermented lactose at a temperature of 22 C. but failed to do 

 so at 37 C. Coplans (1909) found that dulcite was more quickly 

 fermented by certain colon bacilli at 20 C. than at 37 C. 



Rodet (quoted and confirmed by Adami, Abbott and 

 Nicholson, 1899) found that at a temperature of 45 C. B. coli 

 developed in a few hours into long filaments. The same 



