244 
We see clearly how differently the organic substances act 
from carbonic acid. I took home a small piece of cotton wool 
through which the gas had passed for some days. My inten- 
tion was to examine it with the microscope. Less than a 
grain of this cotton was taken out of the tube in which it 
was enclosed, but so thoroughly did the room become offen- 
sive that some friends, not aware of my pursuits, were much 
annoyed. 
This is one of those many facts which lead to the conclusion 
that the amount of carbonic acid is entirely incapable of 
showing the true condition of an atmosphere unless we esti- 
mate that gas at once on its formation, as then it is mixed 
with organic matter. If, however, we allow even a short 
time to pass, a separation takes place, the carbonic acid dif- 
fuses and the organic matter clings to substances to be 
gradually given off : the tendencies of the two arc entirely 
different, and the separation begins at once. 
When the gases were previously passed through charcoal, 
it was difficult to obtain a trace of organic matter. 
I imagine that I see my way now to a very satisfactory and 
comparatively easy investigation, although for the time I 
must leave it to others. 
