AIR BENEATH THE MICROSCOPE. 
169 
At all events, such is the evidence pro and con. We have a 
great deal of valuable testimony in favour of the existence of 
animal and vegetable life in the atmosphere, and a certain 
proportion of that testimony goes to show that contagious 
and infectious diseases may have their origin in atmospheric 
causes ; whilst, on the other hand, we have hardly a tenth part 
of witnesses in favour of the view that the atmosphere is not a 
centre of animal and vegetable life, and that diseases do not 
spread through the assistance of atmospheric germs. We are 
now in a position to examine the latest evidence that has been 
offered on the subject, and to raise one or two objections that 
the whole method of investigation seems to us to be liable to. 
We must now examine Dr. Cunningham’s labours. These 
appear to us to be most valuable, and he has published them 
in a form which, for completeness of detail, for skilful arrange- 
ment, and for excellence and number of illustrations, has cer- 
tainly no equal, at least in our language. Of course the reader 
must be referred to the work itself for the minute accounts. 
We can do little more than sketch in a most imperfect manner 
some of the results at which he has arrived. One of the first 
experiments he describes is of interest, as it shows how many 
different series of animal forms may arise in succession in the 
very same specimen of water which has been at first obtained 
from rain collected at a considerable height above the ground 
(having taken every precaution against uncleanliness), and 
which has been kept for several days perfectly free from the 
admission of the external air. In one specimen (No. II. p. 42 
of Dr. Cunningham’s work) the author found, seventy -two hours 
after it had been sealed, an ample amount of mycelial elements. 
Then two days subsequently (the specimens being regularly 
sealed after examination) he found an abundance of conidia. 
It was then sealed again, left for six days more, with the follow- 
ing results (see fig. 2, Plate CIX.) : — “ The filaments were then 
greatly disintegrated, but the cysts remained very distinct, and 
were present in abundance. They contained a mass of proto- 
plasm marked with one or two granules and clear spaces, the 
latter of which could be seen to alter in number and position. 
In several instances these protoplasmic bodies were observed 
gradually to work their way out of their cysts, which were then 
left behind as extremely delicate rings, hardly visible save with 
careful examination. The process was comparatively slow, and 
the escaping zoospores, for such they seemed to be, shoived a 
well-developed flagellum in active motion for some time before 
they were entirely free. Once detached in the fluid they moved 
actively about by means of the flagellum as well as by free 
amoeboid extensions of their substance, and in many cases the 
flagellum temporally or permanently disappeared, so that, had 
