130 VETERINARY BACTERIOLOGY 



of a toxin as are indicators to the chemist in his study of end- 

 reactions. 



4. Toxins act upon the body by combining chemically with 

 definite cells and tissues. This union is not effected at once 

 in all cases. The evidences of damage, with the clinical symp- 

 toms of poisoning, do not appear until after the lapse of a period 

 of incubation. The length of this period varies with different 

 toxins with some of the snake venoms it is very short, in other 

 toxins it is a matter of hours, or even days. 



5. The injection of non-lethal doses of toxin into a suitable 

 animal causes the tissues to react and to produce antitoxin, 

 which will neutralize the toxin, and result in immunization. 



Toxins may be differentiated from most other poisonous sub- 

 stances with which they may be confused by reference to the 

 preceding. Poisonous alkaloids, such as strychnin, for example, 

 do not cause the production of antibodies. Immunization against 

 a toxin is, therefore, not to be confused with drug habituation. 



Sources of Toxins. Toxins have been found to be produced 

 by a considerable number of plants and animals. Certain of the 

 flowering plants form powerful toxins, such as ricin in the castor- 

 oil bean (Ricinus communis and R. zanzibarensis) , abrin from the 

 jequirity bean (Abrus precatorius) , and robin from the bark of the 

 locust (Robinia sp.). The pollen of certain plants, particularly 

 certain of the grasses, the golden-rod and rag-weeds, is poisonous 

 to some individuals, producing hay-fever, and as specific antitox- 

 ins have been prepared for them, the poison must be regarded as a 

 true toxin. Among the fungi, certain poisonous mushrooms (or 

 " toadstools "), as the Amanita, have been shown to contain toxins. 

 Certain molds are stated to produce toxins, particularly Asper- 

 gillus. Toxins have been demonstrated in the animal kingdom 

 in the venom of snakes, scorpions, and spiders, in the skin of certain 

 reptiles, in the blood of the eel and of certain fish. A few species 

 of bacteria have been shown to produce toxins, but in several cases 

 the amount and character of the toxin are relatively unimportant. 

 The bacteria which have been found to form appreciable amounts 

 of toxin, and which produce lesions of the body tissues through 

 the action of these toxins, are relatively few. The more im- 

 portant are the following: 



