37 
in a room or rooms of ordinary dimensions, an optically 
pure atmosphere, was suggested to me by the results of a 
large number of experiments which I have carried on during 
the last seven or eight years, but more especially the results 
obtained from a series of experiments which I commenced 
about the beginning of this year, on the cultivation ol 
different fungi, the spores of most of which are found in 
large numbers, floating about in our atmosphere. 
Flour paste suggested itself as the best soil I could obtain 
on which to grow the different fungi. When flour paste is 
exposed to the air for a few days, as is well known, fungus 
makes its appearance, and soon completely covers its sur- 
face, and if a number of flour pastes be made and exposed 
in different places, it will be found that different kinds of 
fungus spring up, in each showing a splendid variety of 
different colours, and shades of the same colour. It was 
with a view to isolate and study these different fungi that 
one of my last series of experiments was commenced, and it 
became necessary to look for a means of sowing the seeds 
of each fungus on a soil which should originally be free from 
spore life, and afterwards should be effectually protected 
from the falling of other spores from the air on to the soil, 
and further, should, if possible, give a free and open supply 
of air to the microscopic plants. 
After a few experiments I found that this could be done 
effectually by placing flour paste in an ordinary glass shade 
turned upside down, covering the mouth of the shade with 
a thin layer of cotton wool placed between two pieces of 
cloth, the three layers being fixed round the edges of the 
glass by an elastic band. The paste, when boiled in the 
vessel thus closed, was afterwards found to remain free from 
fungus life for any length of time. Having thus been 
successful by such a rough arrangement in preventing the 
entrance of fungus spores, I next arranged to try the same 
experiment on a rougher and larger scale, and consequently 
