III. 



MODIFICATIONS OF BIOLOGICAL CHARACTERS. 



WE have already referred to the production of an asporogenous 

 variety of the anthrax bacillus. This was effected by Behring by 

 cultivation in media containing small amounts of hydrochloric acid, 

 caustic soda, methyl violet, malachite green, and various other 

 agents. This is only one of many instances of a change in biologi- 

 cal characters due to changed conditions of environment. We have 

 abundant experimental evidence that growth may occur under ad- 

 verse conditions when the species is gradually habituated to these 

 conditions. Thus the temperature limitations may be passed by suc- 

 cessive cultivations at temperatures approaching these limits, and 

 bacteria may grow in the presence of agents which in a given pro- 

 portion have a complete restraining influence upon their develop- 

 ment. For example, in the experiments of Kossiakoff, published in 

 the Annales of the Pasteur Institute (vol. i.), it was found that the 

 several species tested all became habituated to the presence of anti- 

 septic agents in proportions which at first completely restrained 

 their growth. 



This modification of biological characters is well shown in the 

 case of the chromogenic bacteria, some of which only form pig- 

 ment under exceptionally favorable conditions of growth. It has 

 been shown by several observers that iion-chromogenic varieties 

 of some of the best known chromogenic species may be produced 

 by special methods of cultivation. Thus Wasserzug obtained a 

 non-chromogenic variety of the bacillus of green pus (Bacillus 

 pyocyaneus) by the action of time added to that of antiseptics. He 

 says: " These two actions combined have permitted me to obtain 

 cultures which remained without color in a durable way, and in 

 which, consequently, the chromogenic function was abolished by 

 heredity." In the case of a chromogenic bacillus obtained by the 

 writer in Havana (my Bacillus Havaniensis), a non-chromogenic vari- 

 ety was obtained from a culture on nutrient agar which had been kept 

 in a hermetically sealed glass tube for about a year. The variety 

 preserved the morphological characters of the original stock, but, al- 

 



