104 PHYSIOLOGY OF THE BACTERIA. 



Before Pasteur, Ehrenberg and G. de Ciaubry 

 had already announced the presence in the air of 

 the eggs of infusoria. Robin had also recognized 

 that the atmosphere contains, in addition to all 

 sorts of debris, spores, pollen-grains, portions of 

 insects, and rarely the eggs of infusoria. More 

 recently Maddox and Cunningham, by the aid of 

 an aeroscope invented by the former, gathered 

 numerous microbes, as well as bacteroid particles. 

 Tyndall, by causing a ray of light to enter a dark- 

 ened chamber, has rendered visible all these mi- 

 nute corpuscles. His researches show that the 

 optical examination of air enables us to determine 

 in an exact manner the presence or absence of 

 germs. 



Let us also mention the experiments recently 

 made by Miquel in the park of Montsouris. This 

 observer has found in the atmosphere a consider- 

 able number of germs. For the forms of which 

 the diameter exceeds 2 //,, he has ascertained that 

 66 the average number of microbes in the air is 

 feeble in winter and augments rapidly in spring, 

 etc. ; 2. That rain always diminishes the number 

 of these microbes; 3. That rain-water introduced 

 with the greatest precautions, into flasks with slen- 

 der curved necks, first heated to destroy germs, 

 rarely contains rotifers, etc., but always contains 

 bacteria." 



En resume, the existence of germs can be dem- 

 onstrated, 1, by direct research ; and 2, by cultiva- 

 tion. Direct research may be made by the optical 

 examination of the air (method of Tyndall), the 



