116 PHYSIOLOGICAL ACTIVITIES 



same is true of toxins, hence we speak of exo-toxins or toxins 

 excreted from, and endo-toxins or toxins retained within the 

 cell. Among the pathogenic bacteria there are very few 

 which secrete toxins when growing outside the body. 

 Bacilltis tetani or lockjaw bacillus, Bacterium diphtherice or 

 the diphtheria bacillus, Bacillus botulinv^ or a bacillus caus- 

 ing a type of meat poisoning, Pseudomonas pyocyanea or the 

 blue pus bacillus are the most important. Other pathogenic 

 bacteria do not secrete their toxins under the above condi- 

 tions, but only give them up when the cell is disintegrated 

 either within or outside the body. For the reason that 

 endotoxins are therefore difficult to obtain their character- 

 istics have not been much studied. The description of 

 toxins as above given is intended to apply to the exotoxins 

 of bacteria, sometimes spoken of as true toxins, and to the 

 vegetable toxins (phytotoxins) which resemble them. 



The snake venoms and probably most of the animal toxins 

 (zootoxins) are very different substances. (See Chapter 

 XXIX.) 



CAUSATION OF DISEASE. 



This subject belongs properly in special pathogenic bac- 

 teriology. It will be sufficient to indicate that bacteria may 

 cause disease in one or more of the following ways: (a) 

 blocking circulatory vessels, either blood or lymph, directly 

 or indirectly; (b) destruction of tissue; (c) production of 

 non-specific poisons (ptomaines, bases, nitrites, acids, gases, 

 etc.); (d) production of specific poisons (toxins). 



ANTIBODY FORMATION. 



Bacteria cause the formation of specific "antibodies" when 

 properly introduced into animals. This must be considered as 

 a physiological activity since it is by means of substances 

 produced within the bacterial cell that the body cells of 

 animals are stimulated to form antibodies. (See Chapters 

 XXVI-XXIX.) 



