DEVELOPMENT OF THE BACTERIA. 105 
microscopic examination of dust (method followed 
by Marié-Davy, Tissandier), the examination of 
particles obtained by filtration, by gathering germs 
with an aeroscope, by condensation of atmospheric 
moisture upon refrigerating vases, ete. The culti- 
vations consist in exposing to the air which is to 
be examined some liquids in which all pre-existing 
germs have been destroyed (Pasteur, Tyndall, 
etc.). This method has shown that liquids exposed 
in an atmosphere deprived of all germs does not 
undergo putrefaction, but this occurs as soon as 
the access of air not deprived of germs is per- 
mitted (Tyndall). 
All of.these methods give concordant results ; 
deposits containing germs of various kinds are 
always obtained. But this objection presents itself 
to the mind: Do the bacteria obtained by cultiva- 
tion exist in the atmosphere? or do they come 
from germs which have developed rapidly upon 
finding a favorable medium? From the experi- 
ments of Cohn, Miquel, etc., it is known that the 
atmosphere contains very few adult bacteria. Mi- 
quel in a recent communication says, in effect, that 
bacteria are rarely found in the air in a complete 
state, but rather under the form of shining points, 
difficult to distinguish directly one species from 
another. Are not these brilliant points Wicrococei? 
In other terms, the air contains permanent spores, 
organisms which, as we shall see in speaking of the 
reproduction of the bacteria, develop at a certain 
period of the existence of the adult forms, in their 
interior, which escape from the sporogenous fila- 
