462 PATHOGENIC AEROBIC BACILLI 



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 toxae- 

 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. 



89. 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). 



