56 THE ENDOTOXINS 



action on the blood, clumping the corpuscles in a peculiar way, 

 even at a dilution of i : 600,000, and also haemolyzing them. 



Further research leads us to believe that the toxin molecule 

 may be, and under ordinary circumstances is, actually of more 

 complex constitution, being combined with a molecule of true 

 proteid. We have already pointed out the fact that streptocolysin 

 differs in its reactions according to the origin of the serum on 

 which it is grown. The best example, however, is derived from 

 diphtheria toxin when grown in broth containing blood-serum or 

 plasma, and subsequently heated. This solution is but feebly 

 toxic, probably from the toxins having undergone a change into 

 toxoids, yet it possesses the power of immunizing an animal 

 against diphtheria, and of stimulating the production of anti- 

 toxin to an unusual degree, but only on condition that it is 

 injected into an animal of the same species as that from which 

 the serum in which the bacillus grew was obtained. Thus horse- 

 serum toxin will stimulate the production of antitoxin in horses, 

 but not in goats or rabbits, and so forth. We are justified in sup- 

 posing that the essential toxin molecule formed by the diphtheria 

 bacillus exists in this fluid in a state of combination with a specific 

 proteid of horse serum, and that the resulting compound molecule 

 differs from that form when the bacillus is grown in goat serum, 

 in which the essential toxic molecule is united with a different 

 proteid. We may suppose that this essential toxin molecule is 

 produced in Buchner and Uschinsky's asparagin solution, but that 

 it is not produced under ordinary conditions, being in a state of 

 combination with proteid materials of more complex structure. 

 These facts render further research into the chemical nature of 

 the exotoxins of comparatively little importance. 



THE ENDOTOXINS. 



In the case of diphtheria and tetanus and a few other organisms 

 the mode of formation of toxins is a perfectly simple one, and 

 one exactly analogous to the formation of soluble enzymes. In 

 most other cases, however, the facts are less easy to understand, 

 and seem to point to the formation of a toxin which remains 

 under normal circumstances locked up in the substance of the 

 bacteria, just as invertase and diastase are contained within the 

 yeast cell, and not excreted by it into the surrounding fluid. A 

 satisfactory theory as to the nature of these toxins is not forth- 

 coming, and the experimental results obtained by various 



