160 MICROBES, FERMENTS, AND MOULDS. 
apparatus is founded on the principle of the aéroscope, 
invented by Pouchet for the examination of air-dust. * 
It consists of a small cylinder in which a current of 
air is produced by means of an aspirator, on which 
running, water acts, similar to those in use in all 
laboratories of physics and chemistry. A thin plate of 
glass, which has on it a layer of glycerine, is placed 
at the bottom of the cylinder, so as to intercept the 
current of air and arrest the dust. The apparatus 
employed by Miquel at Montsouris is only a modifica- 
tion and improvement of the one devised by Pouchet. 
The glass slide is then transferred to the objective 
of the microscope in order that the dust deposited 
on it may be examined. 
This process has enabled Miquel to define the laws 
which ‘rule the appearance of microbes in the atmo- 
sphere, and he has been able to calculate their number 
in a given volume of air. With respect to such fungi 
and alge as live in our houses (moulds), and on our 
roofs, walls, and on damp ground (such alge as Peni- 
cilliwm, Protococcus, Chlorococeus, ete.), he has arrived 
at the following results, as far as Montsouris, the site 
of his experiments, is concerned. 
Few in number in January and February, the 
number of mould-spores further diminishes in March, 
and rises again in April, May, and June, in which. 
month the maximum is attained. The decrease is slow 
up to October, more marked in November, and the 
minimum is observed in December. In this case the 
