PATHOGENIC AEROBIC BACILLI NOT BEFORE DESCRIBED. 529 
those of another species. Many of the bacilli described in the pre- 
sent section are common saprophytes, which have been shown by 
laboratory experiments to be pathogenic for certain animals when 
introduced into their bodies in a certain amount, which differs greatly 
for different bacteria and for different species of animals. The ex- 
periments of Cheyne and others show how largely the pathogenic 
power of saprophytic bacteria depends upon the quantity of a cul- 
ture which is injected, as well as upon the age of the culture and 
the seat of the inoculation—in the blood, the abdominal cavity, the 
subcutaneous tissues, or the muscles. And the bacteriologist named 
has also shown that pathogenic power depends, in some instances at 
least, upon the combined action of the toxic substances introduced 
in the first instance and of the living bacteria. Thus Cheyne found 
that one-tenth of a cubic centimetre of a bouillon culture of Proteus 
vulgaris injected into the dorsal muscles of a rabbit infallibly caused 
its death within forty-eight hours, but when the dose was reduced 
to one-fortieth cubic centimetre the animal recovered. But if to 
this amount (one-fortieth cubic centimetre) he added one cubic cen- 
timetre of a sterilized (by heat) culture of the same bacillus instead 
of diluting with distilled water, and injected the mixture into the 
dorsal muscles of a rabbit, death occurred in every experiment 
within forty-eight hours. The sterilized culture injected by itself 
produced no effect in this dose (one cubic centimetre), and Cheyne 
believes that the fatal result in these experiments was due to the 
fact that the toxic products present in the sterilized culture over- 
came the natural resisting powers of the tissues and enabled the 
bacillus to multiply over a larger area than would otherwise have 
been the case. As a result of this, toxic substances were produced in 
the body of the animal in sufficient quantity to cause general toxe- 
mia and death ; whereas the bacilli alone, in the dose mentioned, 
were not able to invade the tissues in the vicinity of the point of 
inoculation, and gave rise to a local abscess only. The same ex- 
planation is probably true for very many of the saprophytic bacteria 
which have been shown to possess pathogenic power ; and it is prob- 
able that many of those which are now classed by bacteriologists as 
non-pathogenic would prove to be pathogenic in the same way if 
thoroughly tested upon various species of animals, although it might 
be necessary to use unusually large doses to accomplish the same 
result. 
BACILLUS COLI COMMUNIS. 
Synonyms.—Bacterium coli commune (Escherich); Colon bacillus 
of Escherich ; Emmerich’s bacillus (Bacillus Neapolitanus). Prob: 
ably identical with Bacillus cavicida (Brieger’s bacillus), 
84 
