110 ATLAS OF BACTERIOLOGY. 



in twenty hours. These tests are made best with thin 

 deposits of the spores in water, to which the disin- 

 fectant is added, as we have indicated above in regard 

 to the tests of antiseptic action against bacilli. 



In order to test the resistance of spores to gases it 

 is best to dry them upon pieces of glass ; the gases 

 are allowed to act first in a dry chamber, then in one 

 saturated with water. 



Spores are also less damaged by light than bacilli 

 are; as in the case of bacilli an oxygenated atmos- 

 phere is necessary in order to produce injury by 

 light. Anthrax spores on agar plates were found by 

 Dieudonne to be killed by direct sunlight in three 

 and a half hours (bacilli in one and a half hours) ; 

 when oxygen was excluded they were not injured by 

 exposure for nine hours. 



E. The Effects of Bacteria, Especially in Re- 

 gard to Their Employment for Diagnostic 

 Purposes. 



The effects of bacteria* in vitro may be classified 

 as (1) mechanical; (2) thermal; (3) optic; and (4) 

 chemical. They will be discussed in this order and 

 a fifth section will deal with the effects of bacteria 

 upon the living animal body and will explain the 

 guiding principles necessary to the comprehension of 



* It goes without saying that a classification of bacteria into 

 zymogenous, saprogenous, chromogenous, and pathogenic, is no 

 longer admissible. For example, bacterium coli produces fer- 

 mentation in solutions of sugar, indol and sulphuretted hydrogen 

 in albuminous media, brownish -yellow foci upon potatoes, and is 

 pathogenic to guinea-pigs, i.e., it combines the characteristics 

 of all four groups. 



