224 BACTERIOLOGY 



(4) Those which produce such toxins are not strictly invasive bac- 

 teria. 



(5) The injury due to invasive bacteria is known to be due to the 

 disintegration of bacteria and the setting free of poisons locked up 

 in the bodies of the microbes. 



(6) Pathogenic bacteria manifest less biochemic activity than the 

 related saprophytic forms. 



(7) The hemolytic and leukocidic toxins of bacterial filtrates may 

 be due to autolysis of the bacteria. Jordan has shown that hemolysis 

 is, at least in part, due to a change in the reaction of the culture-fluid. 



According to this hypothesis, micro-organisms, in slowly adapting 

 themselves to the parasitic habit, would gradually eliminate active 

 toxin production and other aggressive weapons as of little use, and 

 strengthen whatever defensive mechanisms they may accidentally 

 possess the rudiments of. If these are capable of marked develop- 

 ment, we may expect such types of disease as tuberculosis, leprosy, 

 glanders, and syphilis, in which the parasitic habit is carried to a high 

 state of perfection. If their mechanisms of defense are not capable 

 of much development, they will soon be destroyed, or else become 

 adapted to live upon the skin, and especially the mucous membrane, 

 as opportunists and occasional disease producers, 



In this adaptation the possession of somatic poisons set free dur- 

 ing disintegration may play an important part. They may give 

 rise to just sufficient toxin to produce a local protecting nidus of 

 necrotic tissue, until the time for escape to some other host arrives. 

 This assumption is supported by the fact that diseases of some 

 duration are usually focal in character. The micro-organisms mul- 

 tiply only in certain foci, which sooner or later become evident as 

 the visible seat of disease. 



It may be claimed that defensive and offensive methods are 

 practically the same, and that it is simply a play upon words to 

 make any distinction between them. But reflection will convince 

 us that offensive methods mean direct injury, whereas defensive 

 methods simply mean a neutralization of the offensive weapons or 

 else a condition which is invulnerable to them, such as an envelope 

 made of a special substance. 



According to Ehrlich and his pupils, the anti-bodies which appear 

 in the course of disease are not new bodies, but overproductions 

 of bodies present in minute quantities normally. The parasitic 

 microbe is thus at the very beginning of the invasion confronted 

 with these bodies. At the termination of the disease there are no 

 new bodies present, but the anti -bodies are on hand in relative 

 abundance. The situation which the invader has to face is thus 

 qualitatively the same at the beginning and at the end of the attack. 

 How does he meet it by defensive methods? 



