BACTERIUM PNEUMONIA. 327 



usually it loses its pathogenic properties after a few 

 generations ; but again this peculiarity may be retained 

 for a much longer time. Not rarely it fails to grow 

 after three or four transplantations on artificial media, 

 though at times it may be carried through many gen- 

 erations. 



INOCULATION INTO ANIMALS. The results of inocu- 

 lations with pure cultures of this organism are also con- 

 spicuous for their irregularity. When the organism is 

 of full virulence the form of septicaemia just described 

 is usually produced, but at times it is found to be totally 

 devoid of pathogenic powers : between these extremes 

 cultures may be obtained possessing every variation in 

 the intensity of their disease-producing properties. 

 The principal pathological conditions that may be pro- 

 duced by the inoculation of susceptible animals with 

 this organism are, according to the degree of its viru- 

 lence, acute septicaemia, spreading inflammatory exuda- 

 tions, and circumscribed abscesses. All three of these 

 conditions may sometimes be produced by inoculating 

 rabbits with the same cultures in varying amounts. 



Rabbits, mice, guinea-pigs, dogs, rats, cats, and sheep 

 are susceptible to infection by this organism. Chickens 

 and pigeons are insusceptible. Young animals, as a 

 rule, are more easily infected than old ones. Rabbits 

 and mice are the most susceptible of the animals used 

 for experimental purposes, and in testing the virulence 

 of a culture it is well to inoculate one of each, for the 

 same culture may sometimes be virulent for mice and 

 not for rabbits, or vice versa. 



If the culture is virulent, intravascular or intra- 

 peritoneal injections into rabbits may produce rapid and 

 fatal septicaemia ; while subcutaneous inoculation of the 



