30 OFFENSIVE FORCES OF INVADING MICROORGANISM 



the body entirely, at the time when the patient is actually dying 

 from the effects of its brief sojourn. Evidently its aggressive forces 

 are minimal, and even though it kills through its highly poisonous 

 toxin, the resistance which the animal body offers to its presence 

 is entirely sufficient to prevent its active development. 



In the case of the diphtheria bacillus similar considerations apply, 

 although the organism, after once it has gained a foothold, is not 

 dependent to the same extent upon outside factors for its existence 

 in the tissues. ^ It may be questionable whether it can gain access to 

 the deeper tissues through intact superficial structures, but through 

 its own toxin it is evidently capable of causing marked destruction 

 after once the superficial epithelial barrier has been passed. Asso- 

 ciated pyogenic organisms may facilitate its growth, but in the 

 deeper structures, at least, their cooperation is not imperative. 

 The diphtheritic exudate may of course extend considerably beyond 

 the original focus of infection, but the infection after all remains 

 a local one in the vast majority of cases. If it becomes generalized 

 at all, this occurs well along toward the fatal end or after death, 

 and is even then relatively insignificant. In the case of this organism 

 also the aggressivity is thus not, as a rule, capable of overcoming 

 the defensive forces of the body, while at the same time it is highly 

 dangerous through its toxin. Evidently the infectious and toxic 

 properties of an organism are two independent factors which in the 

 case of the tetanus and diphtheria bacilli bear an inverse relation 

 to each other. 



True Parasites. An altogether different behavior is seen in a group 

 of organisms which is represented by the anthrax bacillus and the 

 chicken-cholera bacillus. Here the local infection is followed almost 

 immediately by a generalized infection, the organisms not only 

 maintaining themselves, but actually multiplying freely in the body 

 of the host. Their aggressivity, as compared with the so-called 

 necroparasites, is thus extraordinarily developed, while their toxicity 

 is virtually nil. Manifestations of disease are notoriously lacking, 

 while death nevertheless follows. It is remarkable to see rabbits or 

 sheep infected with anthrax bacilli, whose blood is literally swarm- 

 ing with these organisms, quietly feeding and then dying a sudden 

 death without any previous manifestations of disease. We may 

 similarly see guinea-pigs which have been partially immunized 

 against chicken cholera, with the peritoneal cavity a veritable culture 



