9 
But there are other ways of spreadino- the disease that must })e taken 
into account, such as the direct contagiousness of the pneumonic form 
of the disease through the coughing, etc., of the plague-laden s])utum; 
also by the means of fleas and rats. This may account for the exist- 
ence and spread of the disease in such hot countries as the Bombay 
Presidency, Manila, the Island of Mauritius, Kio de Janeii*o, and 
Santos, all of which are in the Tropics and sutler with tropical heat. 
THE EFFECT OF MOISTURE. 
^loisture is a definite factor in the viability of the bacillus 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 quicklv 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 twenW-tive days, when it was still 
virulent for mice. But to be kept alive when dry the organism 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 da 3 ^s. 
EFFECT OF SUNLIGHT. 
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 sunlight plays an important role; also that the effects of 
the sunlight do not penetrate veiy deepl^L It is therefore safe to 
sav that objects may be eflicienth' disinfected on the surface hy expos- 
ing them all da}" to a bright sun, provided the temperature in the sun 
is above 3U° C. 
PLAGUE IN THE SOIL. 
The plague bacillus was kept alive a long time in moist garden earth, 
especially when kept cool. It dies very quickly in dry earth. We 
were not able to keep it alive longer than twenty-four hours at any tem- 
l)erature in dry earth. 
As moist earth will preserve the life of the bacillus it is easy to 
understand how the infection may live in dirty dwellings. It re(juires 
no stretch of the imagination to understand how the infection mav be 
conveved bv the dirt and dust of moist, sunless habitations. 
PLAGUE ON NEW MERCHANDISE. 
We have not succeeded in keeping plague alive very long when 
dried upon the surface of objects; even on })lush, carped. pa])er, wood, 
sawdust, bone, etc., it usually dic's within a b'w days. In porous sub- 
