NOTES AND MEMORANDA. 
193 
In order to assure to these investigations the precision which, as it 
seemed to me, they ought to admit of, I suppressed everything which 
could complicate them ; I substituted for the aeroscopes operating by 
the action of the wind, aeroscopes furnished with a trumpet and a 
meter which would allow the volume of air which entered in a given 
time to be measured. This air, projected by an aperture of half 
a millimetre in diameter upon a drop of a mixture of glycerine and 
glucose, deposited upon it a part of its solid particles. The experiment 
was conducted in the park of Montsouris. The trumpet received 
about 20 litres of air in the hour, and the experiment lasted two days. 
Everything remaining constant, the number of organized cellules 
collected by this process may vary from 500 to 120,000 per cubic 
metre of air, deducting also in this case all bacteroicl particles. If 
so great a divergence exists between the figures published by 
Drs. Maddox and Cunningham, and those which I now give, it is 
obviously to the greater or less perfection of the collecting apparatus 
that it must be attributed. In fact the acroscope of Maddox suitably 
modified gives very good results. Having had an instrument of this 
kind constructed under my directions, I have collected in twenty-four 
hours and by a current of 8 kilometres per hour, nearly 30,000 
microbia, amongst which were 17,000 grains of pollen. The diameter 
of the smallest of the cellules which I take into consideration was not 
less than of a millimetre. 
It is then certain that the atmosphere contains at least a hundred 
times more germs than Drs. Maddox and Cunningham have stated. 
I am equally persuaded that with instruments surpassing in perfection 
those which I now use, the numbers would be very much increased. 
It is necessary to remember that the corpuscles of every kind which 
are thus fixed on a glutinous surface are deposited by a jet of air, 
which only gives up a part and carries away still more with it. 
As the result of my researches I deduce the two following general 
facts applicable to organized corpuscles of the atmosphere whose dia- 
meter is greater than the ythjw of a millimetre. 
1. The average number of microbia of the air, small in winter, 
augments rapidly in spring, remains nearly stationary in summer, and 
diminishes in autumn. 
2. Eain always* provokes the recrudescence of these microbia. 
The increase brought about by rain is not simply sensible, it is 
often surprising. For example, in summer when to great heat 
succeeds a storm, or a rain somewhat sustained, the instruments which 
the day before recorded 5000 to 10,000 germs, record more than 
100,000 the next day. The same fact being moreover reproduced in 
all seasons with a remarkable constancy, I anticipate that new expe- 
riments cannot but confirm the general conclusion. 
Temperature and moisture seem to me (besides purely local 
influences) the principal causes of variation in the number of micro- 
germs in our atmosphere. 
I will not enumerate here the different organisms which the air 
carries. I will content myself with indicating generally those which 
are always found abundantly. 
