236 INFECTION AND IMMUNITY 



positive chemotactic effect on the white blood cells, thereby causing 

 the formation of pus. The nature of the bacterial proteins is by 

 no means clear, and it is still in doubt whether the separation of 

 these substances from the endotoxins can be upheld. 



A number of bacteria may give rise to both varieties of poisons. 

 Thus, recently, Kraus has claimed the discovery of a soluble toxin 

 for the cholera spirillum and Doerr for the dysentery bacillus, both 

 of which microorganisms were regarded as being purely of the 

 endotoxin-producing type. 



It is plain, moreover, that occasionally it may be very difficult 

 to distinguish between a soluble toxin and an endotoxin. In the 

 filtration experiment recorded above, it might well be claimed that 

 the toxicity of the filtrate, when not very strong, may depend upon 

 an extraction of endotoxins from the bodies of the bacteria by the 

 medium. The final test, in such instances, lies in the power of 

 true toxins to stimulate in animals the production of antitoxins; 

 for, as we shall see later, the injection of true soluble toxins into 

 animals gives rise to antitoxins, whereas the formation of such 

 neutralizing bodies in the serum or plasma does not, it is claimed, 

 follow the injection of endotoxins. 



We could spend much time in analyzing the literature on the 

 exotoxin and endotoxin, and this, of course, would be important 

 were we attempting in this book to cover completely immunological 

 problems. When all is said and done, however, the present status 

 of the question is as follows: Certain bacteria, like the diphtheria 

 bacillus, the tetanus bacillus, B. botulinus, some of the anaerobes 

 of surgical infections, etc., produce secretory products during life 

 which are highly toxic, can be obtained during the life of the 

 culture by simple filtration, and which incite, in carefully treated 

 animals, specific neutralizing substances, or antitoxins, which neu- 

 tralize the action of the toxin, roughly according to the law of mul- 

 tiples. These antitoxins in the serum, therefore, can be shown 

 definitely to prevent the injury of the animal by the toxin. 



In many bacteria such soluble toxins cannot be demonstrated. 

 Older bacterial culture filtrates and the bodies of the bacteria may 

 be highly toxic, as in the case of typhoid, cholera, and practically 

 all the Gram-negative organisms, but these toxic substances are 

 derived either from direct extraction of the bacterial bodies, or, as 

 claimed by some, may represent split products produced in the 

 course of decomposition or cleavage of the bacterial protein. These 



