90 BACTERIOLOGY. 



lated a biological law to the effect that every 

 chemical substance which, in a given concen- 

 tration, destroys the life of protoplasm, and in 

 smaller quantity checks development, acts 

 when in still smaller proportions (on the other 

 side of an indifferent point) as a stimulus and 

 increases the vital manifestations. 



In agreement with the above statement is 

 the fact ascertained by Chamberland, Roux 

 and Phisalix, that it is possible, by adding a 

 certain quantity of carbolic acid or chromic 

 acid to anthrax cultures, to destroy the spore- 

 forming property of the germs, and to diminish 

 their virulence or attenuate them to a definite 

 extent. Smirnow and Fliigge have shown 

 that, in general, attenuated microbes are less 

 resistant to chemical influences than virulent 

 cultures. For example, the virulent anthrax 

 bacillus grows well with the addition of four 

 drops of 2 p.c. hydrochloric acid to the nutrient 

 gelatin, but the growth of a slightly attenu- 

 ated bacillus in presence of the same quantity 

 of acid is much retarded and a highly attenu- 

 ated germ does not grow at all. Hammer has 

 found that when pathogenic bacteria are at- 

 tenuated the virulence of the spores is impaired 

 before their power of development has suffered, 

 and Behring has even obtained growth after 

 the spores have lost all power to kill. 



