176 PUBLIC HEALTH BACTERIOLOGY 



bacteria, to be without specific toxic action, but having a 

 positive chemiotactic action on the white cells of the blood, 

 and so preparing the way for the formation of pus. It is 

 still doubtful how much reliance can be placed on the 

 total separation of the soluble and endotoxins from the 

 bacterial protein, and until this doubt is resolved, these 

 conclusions must be accepted with reserve. 



Extracellular Toxins. Of the extracellular or true 

 or soluble toxins, that of B. diphtheriae may be taken as 

 the type. As a class they may be defined as the secretory 

 products of the bacterial cells, passing out into the medium, 

 and soluble therein. That the soluble toxins are only so 

 produced has yet to be proved, and in the meantime they 

 may be ascribed to the following sources, which may occur 

 singly, or in any combination : 



i. vSecretion or excretion from the bacterium. 



2. Action of the bacterium on the medium. 



3. Death of the bacterium and liberation of toxins 



from its disintegrated body. 



The soluble toxins are easily obtainable in large 

 quantities, nevertheless they have not yet been isolated 

 in a pure form, and so our knowledge of them is derived 

 from the study of the complex filtrates in which they are 

 found. Their action is characterized by being selective 

 or specific for certain tissues ; for example, diphtheria, 

 tetanus, and botulismus toxins all attack the nervous 

 system. In the case of many of them, a definite time 

 elapses before symptoms appear after injection. This 

 has been called a period of incubation, though it is suscep- 

 tible of other explanations. The extracellular toxins are 

 apparently uncrystallizable, are soluble in water, are dia- 

 lysable, are precipitated with proteids by absolute alcohol 

 and by ammonium sulphate, are allied to albumoses, and 

 are relatively unstable to heat, light, and chemicals. 



Intracellular Toxins. The endotoxins are either 

 not excreted from the bodies of the bacilli, or are closely 

 bound thereto, or are insoluble in the medium, and remain 

 on filtration on the same side as the bacteria. Any of 

 these theories would account for the known facts in regard 

 to the endotoxins. The greater number of the pathogenic 

 bacteria seem to act by poisons of this class. The poisons 



