BACTERIUM DIPHTHERIA 467 



teria were deposited will be covered with a tolerably firm, 

 grayish-white, loosely attached pseudo-membrane in all 

 respects identical with the croupous membrane observed 

 in the same situation in cases of human diphtheria. In the 

 pseudo-membrane and in the edematous fluid about the 

 skin-wound bacillus diptheriae may be found both in cover- 

 slips and in cultures. 



From what we have seen — ^the localization of the bacilli 

 at the point of inoculation, their absence from the internal 

 organs, and the changes brought about in the cellular ele- 

 ments of the internal .organs — there is but one interpre- 

 tation for this process, viz., that it is due to the production 

 of a soluble poison by the bacteria confined to the site of 

 inoculation, which, gaining access to the circulation, produces 

 the changes that we observe in the tissues of the internal 

 viscera. 



This poison has been isolated from cultures of bacillus 

 diphtheriae, and is found to belong, not to the crystallizable 

 ptomains, but to the toxins — ^bodies which, in their chemical 

 composition, are analogous to the poison of certain venom- 

 ous serpents. By the introduction of this toxin into the 

 tissues of guinea-pigs and rabbits the same pathological 

 alterations may be produced that we have seen to follow 

 inoculation with the bacilli themselves, except, perhaps, 

 the production of false membranes. 



Under certain circumstances with which we are not 

 acquainted bacillus diphtheriae becomes diminished in 

 virulence or may lose it entirely, so that it is no longer 

 capable of producing death of susceptible animals, and may 

 cause only a transient local reaction from which the animal 

 entirely recovers. Sometimes this reaction is so slight as 

 to be overlooked, and again careful search may fail to reveal 



