INFLUENCE OF ILLUMINATING GAS ON BACTERIA AND FUNGI 9 
Bacillus suhtilis.- — This organism was cultivated in the following 
approximate concentrations of illuminating gas: 0.5 percent, 5 per- 
cent, 10 percent, 25 percent, 50 percent, 75 percent, 85 percent, and 
100 percent. In concentrations up to and including 25 percent, 
the colony development, both as to abundance and as to character, 
was practically identical with the development in air. This normal 
growth, as is well known, consists of a white, often wrinkled layer 
on the surface of the agar. The development in 50 percent gas and 
above, however, was quite different in character. The chief difference, 
and perhaps the only one of importance, was the much smaller mass 
of the colony produced. The colony was always very thin, so that 
it never had the opaque character of normal ones. The development 
was confined to the inoculated area and did not extend over the surface 
of the agar as was the case when development was normal. Occa- 
sionally only pin-point colonies were developed, or perhaps nothing 
at all until after return to the atmosphere. Complete sterilization 
practically never took place with an exposure not to exceed ten days; 
but it sometimes took a week or more for development to become 
evident after return to the atmosphere. In those cases where some 
development occurred in the gas it did not proceed further when 
returned to the air, but usually after the lapse of a variable period 
of time an area of normal development began at some point and grew 
over the slant. Inoculations made from these colonies grown in gas 
produced in the air a colony development differing very slightly or 
not at all from the normal in appearance. 
Two series of experiments were run to test the ability of the organ- 
ism to grow continuously in different percentages of illuminating gas. 
In these tests the inoculations after the first were made from cultures 
in the same concentration to which they were to be exposed unless 
no development had taken place in that concentration. In that case 
the inoculation was made from the highest concentration at which 
growth had occurred. In the course of this work, the organism was 
carried through 5 transfers in each of 5 percent, 10 percent, and 25 
percent gas, 3 transfers in 50 percent, 5 transfers in 75 percent and 
85 percent, and 9 transfers in pure gas. It is quite evident, therefore, 
not only that the organism can grow in the gas, but that it can con- 
tinue so to grow for an indefinite time. 
The growing of the organism in the pure gas seems to have caused 
little or no change in it, except in the colony character due to the 
