8 
In these experiments the water was sterile and abundantly inocu- 
lated with a vigorous culture and carefully preserved from contami- 
nation in the dark. In nature the water certainly would not be sterile, 
the effect of sunlight and dilution would play an active part to diminish 
its vitality and infective power. 
THE EFFECT OF TEMPERATURE. 
The effect of temperature upon the bacillus pestis is very remarkable. 
That it is very sensitive to slight changes is well shown in Table A. 
In fact, temperature seems to be the most important factor in the 
viability of the organism. It may be kept alive and virulent a veiy 
long time in the cold, even though dry, but it can not live long when 
dry at the temperature of the body. High temperatures, such as 70° 
C. or more, are invariably fatal in a few minutes. All the published 
experiments agree upon the inffuence of temperature upon this microbe. 
It was this that led some of the early workers to concludethat the v were 
dealing with a frail organism. It is 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 davs when drv at 37° C. — three davs in ffannel, 
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 temperature when kept moist, for 
under such conditions it will live a very long time in albuminous media 
at 37° C. 
PLAGUE AND COLD WEATHER. 
From the experimental studies with the plague bacillus we would 
infer that the endemic foci of plague should be in cold climates. The 
organism dies so rapidly when dried at temperatures above 30° C. that 
we would not expect the disease to be very tenacious in the Tropics. 
This supposition is only partially borne out by the facts. A certain 
number of the endemic foci of plague are in a very rigorous climate. 
Such in particular are the regions of the Garwhal and of Kumaon,^ 
where the disease came from the snow-capped Himalayas. In the 
Transbalkan districts the average temperature in winter is — 20° C. 
In Mongolia the climatic conditions are similar. At Vetlianka during 
the epidemic of plague in 1878-79 the temperature was —12° C. 
PLAGUE IN THE TROPICS. 
Netter states in his ‘‘La Peste et son Microbe” that the disease has 
never invaded the regions where the temperature is tropical, and he 
notes its disappearance in Egypt with the summer. This statement 
would be a confirmation of the fact that the organism does not as a rule 
live outside of the body very long at temperatures of 37° C. and over. 
- Xetter, “ La Peste et son Microbe.” 
