Effects of Bacterial Growth on the Environment 181 



ployed in the treatment of diseases caused by bacterial poisons, 

 and (5) they require an incubation period before clinical symp- 

 toms are apparent. Fever, malaise, and wasting away of animals 

 left untreated are characteristic of biological toxic reactions, 

 whereas chemical poisons, like strychnine, act almost immediately 

 without a preliminary incubation period. 



We think of strychnine as a powerful chemical poison. Yet, 

 the biological toxin produced by Clostriditim tetani (the lock-jaw 

 organism) is two hundred times as potent as strychnine. A guinea 

 pig may be killed by as little as 1/1,000,000 ml. of a bacteria- 

 free filtrate of a culture of Clostridium botulintim—a. highly fatal 

 food-poisoning organism. The route by which toxins gain entrance 

 to the body is vital to the ultimate in vivo (in the body) response. 

 For example, the toxins of botulinum and of certain micrococci are 

 harmful when swallowed, but the poison generated by the diph- 

 theria organisms can conceivably be ingested with little or no 

 systemic reaction in the individual. When diphtheria toxin is in- 

 jected into the bloodstream, however, its lethal effect is directed 

 at the nerve tissues and at heart muscles. Cobra venom can be said 

 to be relatively mild in comparison with the toxin produced by a 

 virulent strain of Conjnehacterium diphtheriae. Exotoxins can be 

 distinguished from each other on the basis of their pharmacological 

 action. Tetanus poison affects motor nerve cells with resultant 

 muscle spasms; botulinum toxin induces early ocular and pharyn- 

 geal paralysis; and diphtheria toxin injected into rabbits causes 

 hemorrhages in the adrenal glands. 



Whereas the diphtheria microbes may localize in the throat, 

 among other places, the poison given off by these localized bac- 

 teria may be carried via the blood stream and the lymph channels 

 to areas of the body directly affected by the poison. The virulence 

 of these exotoxin-producing species is directly dependent upon 

 their ability to form and to liberate their powerful poisons. 



Roux and Yersin in 1889 first discovered diphtheria toxin, and 

 they demonstrated that this lethal agent in the filtrate of broth 

 cultures was capable of producing the same symptoms in laboratory 

 animals as an injection of the living microbes. This opened up the 



