14 
C. A. LUDWIG 
paler color than normaL The organism grew in all the gas-air mixtures 
used — 5 percent, lO percent, 25 percent, 50 percent, 75 percent, and 
85 percent gas — but not in pure gas. The 5 percent and usually the 
10 percent concentration did not show any toxic effect, but at 25 per- 
cent of illuminating gas the development was always checked. At 
75 percent and 85 percent the development was , very slow and the 
colony quite pale, sometimes nearly colorless. Normally an exposure 
in pure gas was followed by development within a week when returned 
to the air, but in a few cases an exposure of a week or less seemed to 
sterilize the material, since no development had taken place in 13-18 
days. The organism was carried through 5 transfers in 5 percent, 
10 percent, 25 percent, and 85 percent gas, 3 transfers in 50 percent, 
and II transfers in 75 percent. 
Penicilliiim stoloniferum. — This species grows rather rapidly on 
the medium used and soon becomes green with the large number of 
conidia produced. This color soon changes to some shade of brown, 
and later the colony is often overgrown with hyphae from underneath. 
The checking effect of unfavorable conditions can often be detected 
for several days after conidia production by means of the younger 
appearance of the retarded cultures as compared with the check. 
Development occurred in 5 percent, 10 percent, 25 percent, 50 percent, 
75 percent, and 85 percent gas, but not in pure gas. It was quite 
normal in character to 50 percent but was much slowed down at that 
concentration. The checking of growth was observed at 10 percent 
but not at 5 percent. At concentrations of 75 percent and above 
development was slow and did not extend very far laterally, while a 
good many of the spores were apparently killed. As a result a cushion- 
shaped or roughly hemispherical mass of apparently upright hyphae 
was produced at each point of inoculation. The entire slant, therefore, 
often contained these pulvinate colonies, which sometimes reached a 
diameter of 2 or 3 mm. and became more or less confluent. Conidia 
were not produced under such circumstances except in one or two 
instances in which it is doubtful if the percentage of gas had been 
maintained. Even after the return of these cultures to the air there 
was only exceptionally any conidia production or other growth, 
although new cultures inoculated from them and kept in the air 
developed conidia normally. Cultures prevented from developing by 
being exposed to pure gas grew and produced conidia as usual in some 
cases upon being returned to the air. The species was maintained 
