PRODUCTION OF TOXINS 113 



stances of rather large molecule and are precipitated by 

 many of the reagents which precipitate proteins. Toxins 

 will be further discussed in Chapter XXVII. It will be 

 sufficient at this point to enumerate their chief peculiarities 

 in order to show their marked resemblance to enzymes. 



1. Toxins are dead organic chemical substances. 



2. They are always produced by living cells. 



3. They are active poisons in very small quantities.^ 



4. Their action is specific in that each toxin acts on a 

 particular kind of cell. The fact that a so-called toxin acts 

 on several different kinds of cells possibly indicates a mix- 

 ture of several toxins, or action on the same substance in the 

 cells. 



5. Toxins are very sensitive to the action of injurious 

 agencies such as heat, light, etc., and in about the same 

 measure that enzymes are, though, as a rule, they are some- 

 what more sensitive or "labile." 



6. Toxins apparently have maxima, optima and minima 

 of temperature for their action, as shown by the destructive 

 effect of heat and by the fact that a frog injected with 

 tetanus toxin and kept at 20° shows no indication of poison; 

 but if the temperature is raised to 37°, symptoms of poison- 

 ing are soon apparent. Cold, however, does not destroy a 

 toxin. 



7. When properly introduced into the tissues of animals 

 they cause the body cells to form antitoxins (Chapter 

 XXVII), which are capable of preventing the action of the 

 toxin in question. 



8. The determining test for a toxin is its action on a living 

 cell. 



It is true that enzymes are toxic, as are also various 

 foreign proteins, when injected into an animal, but in much 

 larger doses than are toxins. 



A marked difference between enzymes and toxins is that 

 the former may bring about a very great chemical change 

 and still may be recovered from the mixture of substances 

 acted on and produced, while the toxin seems to be perma- 



Tetanus toxin is about 120 times as poisonous as strychnin, both of which 

 act on the same kind of nerve cells. 



8 



