338 BACTERIOLOGY. 



gous to the poison of certain venomous serpents. By 

 the introduction of this toxalbumin, as it is called, into 

 the tissues of guinea-pigs and rabbits the same patho- 

 logical alterations may be produced that we have seen 

 to follow the result of inoculation with the bacilli them- 

 selves, except, perhaps, the production of false mem- 

 branes. 



Under the influence of certain circumstances with 

 which we are not acquainted the bacillus diphtheria be- 

 comes diminished in virulence or may lose it entirely, 

 so that it is no longer capable of producing death of 

 susceptible animals, but may cause only a transient local 

 reaction from which the animal entirely recovers. Some- 

 times this reaction is so slight as to be overlooked, and 

 again careful search may fail to reveal evidence of any 

 reaction at all. This exhibition of the extremes of its 

 pathogenic properties, viz., death of the animal, on the 

 one hand, and only very slight local effects on the other, 

 was at one time thought to indicate the existence of two 

 separate and distinct organisms that were alike in cul- 

 tural and morphological peculiarities, but which differed 

 in their disease-producing power. Further studies on 

 this point have, however, shown that the genuine bacil- 

 lus diphiherice may possess almost all grades in the 

 degree of its virulence, and that absence of or diminu- 

 tion in virulence can hardly serve to distinguish as sep- 

 arate species these varieties that are otherwise alike; 

 moreover, the histological conditions found at the site 

 of inoculation in animals that have not succumbed, but 

 in which only the local reaction has appeared, are in 

 most cases characterized by the same changes that are 

 seen at autopsy in animals in which the inoculation has 

 proved fatal. 



