292 Transactions of the Royal Microscopical Society. 
parts easily reduced to a powdery state. It had been dried at 
150^ Falir., and the dust was exposed to 145° Fahr. for fifteen 
minutes. This dust was now carefully mixed with some taken 
from the infusion in which the large calycine form had been, 
which I had before used. I determined to take no notice of the 
" springing monad " on this occasion, but confine my observations 
to the two contrasted forms — the minute " uniflagellate," whose 
spore, as I have said, at first, is invisible ; and the comparatively 
large calycine " form, with proportionately larger spore. 
The powders were very intimately mixed, and difi'used by long 
continued commotion of the contained air as evenly as possible 
through the chamber. When the larger particles had fallen, nine 
cups of the fluid were inserted. Only three of them were open, 
the remaining six having the covers on as before. At the end of 
twenty-four hours two of the covered vessels were exposed by 
the removal of the covers ; and at the expiration of forty-two hours 
the remaining four were all uncovered. When each set had in 
turn been undisturbed for five days, they were subjected to careful 
examination. The first three yielded both forms of monad in 
every drop taken — the number of which was twenty from each 
basin ; so that in sixty test-drops both the large (calycine) and the 
small (uniflagellate) monad appeared almost in equal proportions. 
The next two cups which had been uncovered at the end of 
twenty-four hours, showed the small monad in every drop ; thirty 
drops being taken from each cup ; but the calycine or large 
monad, only was seen in one drop out of the whole (sixty). 
The remaining four vessels were then most carefully examined, 
thirty drops being taken from each vessel. The result was that 
the small monad appeared in full vigour in every drop examined, 
and the large form was not found at all. 
Finally, four carefully cleaned vessels were partially filled with 
the nutritive fluid, and put into the chamber, covered, when the 
last of the above series were taken out, and when the beam showed 
that the air in the chamber was quite moteless. The covers, how- 
ever, were not withdrawn for twelve hours, that all might be as 
safe as possible. The open vessels were then left five days, and 
examined ; but not a trace of a monad was seen in any drop taken 
from either of the vessels ; and bacteria, which had been more or 
less present in every instance, were only sparsely, in this instance, 
to be seen. 
The inference appears to be irresistible. The germs of minute 
and widely-diffused organic forms of a septic nature may be present 
in enormous quantities in the air, and their presence may be 
demonstrated, for when they are optically proved to be present, 
their origin being known, they are seen to germinate in suitable 
fluids, while the same fluids in their absence are, under the same 
