106 A MANUAL OF BACTERIOLOGY 



are immutable. The stability of her processes, the 

 precision of her action, and the universality of her 

 laws, are the basis of all science, to which biology 

 forms no exception. Once establish, by clear and 

 unmistakable demonstration, the life-history of an 

 organism, and truly some change must have come 

 over Nature as a whole, if that life-history be not 

 the same to-morrow as to-day ; and the same to one 

 observer, under the same conditions, as to another. 



'But the fact that there is no evidence of any 

 direct relation evolutionary between two such 

 forms as Bacillus subtilis and Bacillus anthracis, the 

 fact that there is no ready way either naturally or 

 artificially of their being changed into each other, 

 must not blind us to the fact that such an evolutional 

 relation in the past is eminently probable, nay almost 

 certain. It may, in all probability must, have 

 taken an indefinite time in the past to effect ; but 

 being once effected, the specificity is continued as 

 in every other form by inheritance.' 



There are certain conditions under which a 

 microbe may appear to have altered its properties. 

 For instance, Chauveau 1 has shown that Bacillus 

 anthracis loses its virulence when submitted to the 

 action of compressed oxygen ; but it does not lose 

 its vaccinal property after this treatment. This new 

 character is said to be maintained by suitable 

 cultivation. Although Bacillus anthracis may lose 

 its virulence under such abnormal conditions as 

 already alluded to, it does not become a non-patho- 

 genic microbe, for it still preserves one of the most 



1 Comptes Rend/us de P Academic de* Sciences, tome 109. 



