INFLUENCE OF ILLUMINATING GAS ON BACTERIA AND FUNGI 1 9 
Species. None of the values indicating retardation at lO percent or 
below is significantly smaller than the value for its check except for 
Endothia fluens at about lo percent. The lower limit for retardation 
of E. fluens^ therefore, would seem to be somewhere between 5 percent 
and 10 percent. The retarded cultures, after being returned to the 
air, grew at approximately the same rate as the regular air cultures, 
thus demonstrating that after-effects are usually lacking; except that 
no development occurred in any case in any plate which had been 
exposed to pure gas. 
Some of the cultures, including the two species of Endothia and 
Fusarium radicicola, produced in the toxic amounts of gas a more com- 
pact, velvety, deeper colony, with the hyphae more erect than in air. 
It is likely that these hyphae have interesting morphological char- 
acteristics induced by the treatment, but opportunity was not found 
to investigate this feature. 
It seems clear, therefore, that among the organisms studied, 
including 13 species of bacteria and 11 species of fungi, there is no 
example of the extreme sensitiveness to illuminating gas which is 
displayed by some phanerogams. 
2. Methane 
Production and Purification of the Gas 
It was found difficult to get methane of sufficient purity for the 
tests conducted. The best way to produce it is said to be to treat 
aluminium carbide with water; but owing to the war no aluminium 
carbide could be obtained. Some of the gas was prepared from methyl 
iodide by means of the copper-zinc couple. This gas was quite toxic 
to the organisms but had a distinct odor. It was therefore feared 
that some unchanged methyl iodide vapor passing over with the gas 
had been incompletely decomposed by the tower of zinc through 
which it had passed and that the reactions were due to this methyl 
iodide vapor. Some trials with methyl iodide vapor were accordingly 
conducted, and the results were corroborative of the fear just men- 
tioned. The method finally settled on for preparing the gas with 
which most of the tests were conducted was the ordinary sodium 
acetate-soda lime method with barium oxide substituted for the 
soda lime. This method is said in some of the organic chemistry 
texts to produce nearly pure methane. In the earlier experiments 
