10 
C. A. LUDWIG 
slowing down of growth to a very low point. This is evidenced by 
the fact, mentioned above, that a culture from a line previously 
carried in the air developed as well in the gas as another culture from 
a line previously carried in gas. It is also evidenced by the fact that 
in the first transfer into the air after a period of several transfers in 
gas the colony growth was normal in appearance in all respects. The 
examination of stained microscopic mounts supported the foregoing 
evidence. Bacteria from air cultures one day old and ii days old 
and from a gas culture ii days old were stained. In size, shape and 
especially in the absence of spores the bacteria of the gas culture 
(ii days old) resembled those of the one-day air culture more than 
they did those of the ii-day culture. There were only a few spores 
in the one-day culture, none in the ii-day gas culture, but most of 
the structures in the ii-day air culture were spores. 
Bacillus pyocyaneus. — The culture of B. pyocyaneus used in this 
study developed the color only rarely. The color has therefore not 
been used as a character on which to base comparisons, although it 
has been so used in the past. The typical colony growth was rather 
dirty white, semi-translucent in character; and it was often difficult, 
because of the indefinite tint of the colony, to detect differences in 
the development of the growths under comparison. This organism 
was first grown in 5 percent, 50 percent, and 85 percent gas. The 
development was quite normal in 5 percent gas, but proceeded more 
slowly in the higher concentrations, so that whereas it took about 
three days for a culture in air to reach its maximum, it took two to 
three days longer for the 85 percent gas culture to reach the same 
stage. Attempts at this time to grow the species in pure illuminating 
gas met with three clear-cut failures and one apparent success, which, 
however, was possibly due to failure to displace all of the air in the 
container. In one of the cases of failure the organism developed 
(after a 4-day exposure) when returned to the air, but in the other two 
(after exposures of 6 days and 3 days) it did not develop within periods 
of 16 days and 27 days respectively. In later experiments, as will 
be shown presently, the attempt to cultivate the organism in pure gas 
resulted successfully. There was little or no alteration in the colony 
character in the gases, provided a colony was produced. 
It was found also that the organism can apparently be carried 
indefinitely in most of the gas concentrations and perhaps even in 
pure gas. It was carried through 5 transfers in 5 percent, 10 percent, 
