418 M. ARMAND BUFFER. 



death .^ A few drops only of a culture of the Bacillus pyo- 

 cyaneus injected into the veins of a rabbit give rise to a 

 chronic disease ; whereas a quarter of a cubic centimetre of 

 the same culture kills the animal with certainty.^ One cubic 

 centimetre of an emulsion of the culture of the Bacillus 

 prodigiosus in beef-broth produced no eflFect on a rabbit;^ 

 whereas 3 cubic centimetres of the same emulsion proved fatal 

 to another animal. 



Another and most important factor is the virulence of the 

 micro-organisms introduced into the system. Without entering 

 at present into the question of the means by which the viru- 

 lence of microbes can be raised or lowered, or into the other 

 question as to what is really meant by virulence, it is a well- 

 ascertained fact that this factor varies within very wide limits. 

 The same number of anthrax bacilli contained in a drop of 

 blood from an animal dead of anthrax, in a drop of Pasteur's 

 first or of his second vaccines for the same disease, gives 

 rise to widely different effects if introduced into three animals 

 of the same species. The disease produced in rabbits by the 

 injection of a culture of the bacillus of fowl cholera ten days 

 old differs widely from that produced by the injection of a cul- 

 ture one day old. One might say almost that the virulence of 

 a given species of micro-organism is inversely proportionate to 

 the number of microbes necessary to kill a given animal. 



The species of animal used for the experiments is, perhaps, 

 of still greater importance than the quality of the virus. 

 Rabbits inoculated with the bacilli of fowl cholera, of anthrax, 

 or of diphtheria, speedily succumb to these diseases, but 

 the injection of cultures of quarter-evil or typhoid fever has 

 no effect on these same animals. Guinea-pigs, on the other 

 hand, perish quickly when the bacillus of quarter-evil is in- 

 jected into them. The inoculation of the bacillus of anthrax 

 into a number of European sheep is followed by the death of 



' Odo Bujwid's numbers arc somewhat higher, but this docs not alter the 

 truth of the fact. 



- Charrin, ' La Maladie Pyocyanique,' Paris, 1889. 

 3 M. Armand Ruffer, unpublished observations. 



