APRIL 25, 1884.] 
air, however humid this may be. It is most 
abundant in spring and summer, and almost 
disappears during the autumn and winter. 
During the summer it exists to the number of 
from five thousand to ten thousand in every 
cubic metre of the atmosphere. 
The spores of the cryptogams and algae 
appear during the damp months of April and 
May, and reach their greatest numbers in the 
latter part of June. ‘They persist during the 
summer, and fall off during the autumn, to 
become as rare in winter as the pollen. The 
number varies from seven thousand in a cubic 
metre in December, to thirty-five thousand in 
summer. Fluctuations are found dependent 
upon damp or dry weather, the action of which, 
however, differs with the time of year. During 
‘a cold and wet period in winter, the spores 
sink to their minimum, while during the dry 
time the air is greatly enriched, but chiefly by 
old spores. In the summer, on the contrary, 
during damp days, the fructifications of the 
cryptogams are everywhere distributed in abun- 
dance. 
‘“The average of the spores collected by the aero- 
scope is about fourteen thousand per cubic metre. 
These figures are not excessive, and it is to be hoped 
that they will settle the contradictory opinions in 
this regard which have been expressed during the 
past twenty years. They will go to confirm in their 
ideas the partisans of the germ-theory, and will show 
to the few defenders of spontaneous generation how 
useless it is to invoke the doctrine of heterogenesis 
to explain the appearance of the mucidines in the 
liquids and on the substances fitted to maintain their 
hife.’’ 
From an etiological and hygienic point of 
view, it does not seem that such diverse spores, 
introduced into the economy at the rate of 
thirty thousand a day, or one hundred million 
a year, are absolutely innocuous. The develop- 
ment of soor in the mouths of infants and in 
the respiratory tract of the dying show that the 
fungi also belong to parasites ready to invade 
the human organism when there is presented a 
point of feeble resistance. 
The analysis of the air taken from the sew- 
ers showed about the same amount of orga- 
nized material, with the exception of the almost 
entire absence of starch. 
The remainder of the book is devoted to a 
study of the bacteria present in the air. This 
is the part which will naturally be of the great- 
est interest, from the relations which these 
minute organisms bear to disease and to the 
_ processes of putrefaction and fermentation. 
Chapter iii. is devoted to a statement of the 
experiments of Pasteur and others, proving 
conclusively the existence of germs in the air, 
SCIENCE. 
a19 
which alone are responsible for changes in the 
liquids into which they fall, and thus setting at 
rest the question of ‘ spontaneous generation.’ 
The classification of the bacteria receives a 
valuable contribution as the result of long and 
carefully conducted experiments. The author 
is convinced of the immutability of the species, 
but shows that they are capable of great varia- 
tions under different conditions, and that with- 
out great watchfulness ‘ species’ can be easily 
multiplied. The genera which are usually 
recognized, and which he accepts, are Micro- 
coecus, Bacterium, Bacillus, Vibrio, and spi- 
ral Microbia. Even these genera cannot always 
be distinguished apart with certainty by their 
form alone. The characters which serve to 
differentiate them are briefly ‘as follows: Mi- 
crococci and Bacteria never produce spores, 
Bacilli do; Micrococci are immovable, Bac- 
teria are movable; Vibrios and Spirilla have 
an undulated or twisted form. 
The methods of obtaining the spores from 
the air, and the sterilization and preparation 
of the liquids proper for their development, 
are the subject of the next chapter. This, as 
all other parts of the work, shows the results 
of infinite care and patience. National preju- 
dice is, perhaps, the reason why the solidified 
meat-extracts and blood-serum have not been 
employed for the cultivation of the spores. 
But it is perhaps fortunate for the progress 
of science that such prejudices exist, as each 
method is developed to its greatest extent, and 
the exact value of the one can be controlled by 
the other. The liquid nutritive material has 
certainly received a most thorough trial in the 
hands of Mr. Miguel, and the results obtained 
by its use are not to be thrown lightly to one 
side. ‘There are infinite sources of error when 
experimenting with the ‘infinitely small ;’ and 
the precautions which have been found neces- 
sary from these extended observations should 
caution those observers who have only limited 
means at their command against hasty gener- 
alization. One of the most important safe- 
guards is the proper ‘ firing’ of the flasks which 
are to receive the culture. Experience has 
shown that they should be heated during four 
hours at 200° C.; and then, after having been 
charged with the ‘ bouillon,’ they should stand 
for two months at 35° C. in a constant tempera- 
ture apparatus. At the end of that time those 
which have retained their limpidity are regard- 
ed as sterile, and ready to be sown. 
In order to obtain the number of spores dis- 
tributed in the atmosphere, equal amounts of 
air are drawn over these sterilized solutions, 
and are then allowed to germinate at a constant 
