184 THE AMERICAN MONTHLY [July 
TEMPERATURE.—The effect of. temperature upon the 
bacillus pestis is very remarkable. It may be keptalive 
and virulent a very long time in the cold, even though 
dry, but it cannot live long when dry atthe temperature 
of the body. High temperatures, such as 70° C. or more, 
are invariably fatal in a few minutes. It was this that 
led some of the early workers to conclude that they were 
dealing with a frail organism. - ltis frail when dried at 
37° C., but may live for months in the cold. We have 
never been able to keep it alive more than a few days 
when dry at 37° C.—three days in flannel, two days in 
sponge. On the contrary we had little difficulty in keep- 
ing it alive on a variety of objects three and four months 
at 17° to 19° C. The bacillus is not as sensitive to tem- 
perature when kept moist, for under such conditions it 
will live a very long time in albuminous media at 37° C. 
From the experimental studies with the plague bacillus 
we would infer that the endemic foci of plague should be 
in cold climates. 
Moisture is a definite factor in the viability of the ba- 
cillus pestis, The organism must have moisture to grow, 
and it may remain alive and virulent a very long time in 
the presence of moisture. It usually dies quickly when 
dry. However, this is not invariably the case. We have 
been able to keep it alive in media such as dried albumin 
for one hundred and twenty-five days, when it was still 
virulent for mice. But to keep it alive when dry the or- 
ganism must be cold, i. e., exposed to a. temperature less 
‘than 20° C. In no instance could the organism be kept 
alive when dry at a temperature of 37° C. for more than 
a few days. 
Our experiments confirm those of other workers in this 
field, who find that for the most part the bacillus pestis 
soon dies when exposed to bright sunlight. Our work 
leads us to the conclusion that the heat as well as the sun- 
light plays an important role; also that the effects of the 
