160 MICROBES, FERMENTS, AND MOULDS. 



apparatus is founded on the principle of the aeroscope, 

 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 algae as live in our houses (moulds), and on our 

 roofs, walls, and on damp ground (such algae as Peni- 

 cillium, Protococcus, Chlorococcus, etc.), 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 



