6 
ism, resistant to influences usually detrimental to bacterial life, or one 
that loses its virulence and dies quickly when removed from its natural 
habitat. 
The bacillus of plague does not exist in nature on sterile glass cover 
slips, nor yet in the desiccator over concentrated sulphuric acid, which 
were conditions used by some authors who have reported their results 
on this question. 
It is also necessary to call attention to certain conditions which 
obtained in most of these experiments, that are very far from the usual 
state of affairs. 
The test objects were very abundantl}^ inoculated with a pure cul- 
ture of the bacillus pestis of known activity and virulence. Often the 
test objects were saturated. The cultures had been grown for a long 
time upon artiflcial media in the laboratory, so that their vitality was 
probably strongly influenced. It is a well-known fact that virulent 
pathogenic bacteria may at first grow ver}^ poorly upon the ordi- 
nary lalioratory media, but by successive cultivation they become 
accustomed to the new conditions, so that they finally thrive abund- 
antly; that is to say, they take on a sort of saprophytic existence. 
Such cultures would doubtless resist the various influences to which 
the}^ are exposed in the laboratory tests better than another race direct 
from the blood or tissues. In fact, it is found that the plague bacillus 
in the blood and tissues from a rabbit usually dies out rather quickly 
when dried upon the test objects. On the contrary, bouillon cultures 
dried on similar objects and under similar conditions live a much 
longer time. 
Another departure from normal conditions was the fact that all the 
test objects receiving the abundant inoculations of the virulent pure 
cultures were sterile. In other words, not only were cultures of the 
bacillus used that were accustomed to a saprophytic existence, but 
these cultures were placed upon sterile test objects and protected 
against contamination, so that they were relieved from that microbial 
symbiosis which, in the economy of nature, plays so important a part 
in the suppression of pathogenic micro-organisms. It is known that in 
organic mixtures the hardier saprophytes tend to overpower the 
bacillus pestis. This even occurs to a certain extent in the blood and 
buboes of patients sick of the disease, as well as in dead organic infu- 
sions. The bacillus pestis is not known to have synergists among the 
lower forms of life. But that such exist may well be inferred from 
analogy. 
Further, different races of the plague organism have different pow- 
ers of resistance to unfavorable influences. Some races of plague are 
hardier than others, just as some races of mankind are hardier than 
others. Batzerofi states, ‘‘There undoubtedly exist varieties that 
attenuate very quickly and^die outside the living body in a relatively 
