DEVELOPMENT OF THE BACTERIA. 105 



microscopic examination of dust (method followed 

 by Marie-Davy, Tissandier), the examination of 

 particles obtained by filtration, by gathering germs 

 with an aeroscope, by condensation of atmospheric 

 moisture upon refrigerating vases., etc. 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 Micrococcif 

 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- 



