114 PHYSIOLOGICAL ACTIVITIES 



nently used up in its toxic action and cannot be so recovered. 

 Toxi?!^ seem very much like enzymes whose action is restricted 

 to living cells. 



Just as enzymes are probably produced by all kinds of 

 cells and not by bacteria alone, so toxins are produced by 

 other organisms. Among toxins which have been care- 

 fully studied are riciyi, the poison of the castor oil plant 

 (Ricimis communis)) abrin of the jequirity bean (Abrus pre- 

 catorius) ; robin of the common locust ( Robinia pseudacacia) ; 

 poisons of spiders, scorpions, bees, fish, snakes and sala- 

 manders. 



It has been stated that some enzymes are thrown out 

 from the cell and others are retained within the cell. The 

 same is true of toxins, hence we speak of exotoxins or toxins 

 excreted from and endotoxins or toxins retained within the 

 cell. Among the pathogenic bacteria there are very few 

 which secrete toxins when growing outside the body. Clostri- 

 dium tetani or lockjaw bacillus, Corynebacterium diphtherice or 

 the diphtheria bacillus, Clostridium botulinum or a bacillus 

 causing a type of food poisoning, Pseudomonas aeruginosa or 

 the blue pus bacillus are the most important. Other patho- 

 genic bacteria do not secrete their toxins under the above 

 conditions, but give them up only when the cell is disinte- 

 grated either within or outside the body. For the reason 

 that endotoxins are therefore difRcult to obtain, their char- 

 acteristics 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 (phy to toxins) 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 



