FACTORS OF PATHOGENICITY AND INFECTION 187 



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 stimu- 

 late 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. This distinc- 

 tion will become clearer as we proceed in the discussion of immunity. It 

 must not be forgotten, however, that our knowledge of bacterial poisons 

 is by no means complete, and that sharp distinctions as those given above 

 must be regarded to a certain extent as tentative. 



In resistance to chemical action and heat, the various poisons show 

 widely divergent properties. As a general rule, most true soluble 

 toxins are delicately thermolabile, they are destroyed by moderate 

 heating, and deteriorate easily on standing. Their chemical nature is 

 by no means clear, but, on precipitation of toxic solutions with mag- 

 nesium sulphate, these poisons come down together with the globulins. 

 The nature of the endotoxins is still less clearly understood. Most of 

 them, while less labile than the extracellular poisons, are, nevertheless, 

 destroyed by exposure to 70 C. On the other hand, certain specific and 

 powerful intracellular poisons, like those of the Gartner bacillus of meat 

 poisoning, may undergo exposure \,o even 100 C. and still retain their 

 toxic properties. The nature of each individual poison will be discussed 

 in connection with its microorganism. 



The Mode of Action of Bacterial Poisons. Close study of the toxic 

 products of various microorganisms has shown that many of the bac- 

 terial poisons possess a more or less definite selective action upon special 

 tissues and organs. Thus, certain soluble toxins of the tetanus bacillus 

 and Bacillus botulinus attack specifically the nervous system. Again, 

 certain poisons elaborated by the staphylococci, the tetanus bacillus, 

 the streptococci, and other germs, the so-called " hemolysins," attack 

 primarily the red blood corpuscles. Other poisons again act on the 

 white blood corpuscles; in short, the characteristic affinity of specific 

 bacterial poisons for certain organs is a widely recognized fact. 



In explanation of this behavior, much aid has been given by the 

 researches of Meyer, 1 Overton, 2 Ehrlich, 3 and others upon the causes for 



1 Meyer, Arch. f. exper. Pathol., 1899, 1901. 



2 Overton, "Studien lib. d. Narkose," Jena, 1901. 



3 Ehrlich, "Sauerstoffs-Bediirfniss des Organismus," Berlin, 1885, 



