104 PHYSIOLOGY OF THE BACTERIA. 
Before Pasteur, Ehrenberg and G. de Claubry 
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 débris, 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 p, he has ascertained that 
“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 résumé, 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 
