186 THE AMERICAN MONTHLY [July 
on paper allowed to dry, and fourteen days on paper kept 
in a moist atmosphere. To live this long it must be kept 
cool, for, just as in all our other experiments, it died very 
quickly when dried at the body temperature. We had 
similar experiences with plague blood upon paper. 
The bacillus pestis often loses its virulence before it 
dies. In many of our experiments we found that the time 
came when the organism grew in bouillon, but lost its 
pathogenity for animals. This is an important fact from 
an epidemiologic standpoint, for an attenuated plague ba- 
cillus is probably harmless to man, even though its viru- 
lence be increased by artificial means in the laboratory. 
The experiments conducted in this laboratory plainly 
prove that either sulphur dioxide, when moist, or form- 
aldehyde will kill the bacillus pestis when applied in the 
strength and methods usually employed for these gases 
as disinfecting agents. In order to be effective there must 
be directed contact between the gas and the germ. In 
other words, these gaseous disinfectants can only be de- 
pended upon as surface disinfectants. 
As far as practical disinfection for plague is concerned, 
it may be mentioned here that sulphur dioxide is proba- 
bly a much more useful agent for use of ships, stores, 
houses, and dwellings infested with vermin, because it is 
destructive to the higher forms of animal life, whereas 
formaldehyde fails to kill mammals and insects with the 
same certainty that it kills microbes. In combating plague 
it is very important to kill fleas, rats, mice, and other 
forms of animal life capable of carrying the infection. 
Sulphur has this power, which formaldehyde totally 
lacks. A great number of tables exhibit details of exper- 
iments which cannot be reported here. 
CONCLUSIONS. 
1. The bacillus pestis is not a frail organism. It re- 
sembles the hemorrhagic septicemic group or the cocco- 
bacilli as far as its viability is concerned. 
