94 PRINCIPLES OF BACTERIOLOGY 



at 55 C. nearly the whole of it will be coagulated. Such considerations 

 suggest that the relation of toxic action to fermentation must be left an 

 open question. 



SIMILAR VEGETABLE AND ANIMAL POISONS. Within recent years 

 it has been found that the bacterial poisons belong to a group of toxic 

 bodies all presenting very similar properties; other members of which 

 occur widely in the vegetable and animal kingdoms. Among plants 

 the best-known examples are the ricin and abrin poisons, obtained by 

 making water emulsions of the seeds of the Ricinus communis and the 

 Abrus precatorius (jequirity), respectively. The chemical reactions of 

 ricin and abrin correspond to those of the bacterial toxins. They are 

 soluble in water; they are precipitable in alcohol, but being less easily 

 dialyzable than the albumoses they have been called toxalbumins. 

 Their toxicity is seriously impaired by boiling, and they also gradually 

 become less toxic on being kept. Both are among the most powerful 

 poisons known, ricin being the more fatal. 



It is also certain that the poisons of scorpions and of poisonous snakes 

 belong to the same group. The poisons derived from the latter are 

 usually called venins, and a very representative group of such venins 

 derived from different species has been studied. To speak generally, 

 there is derivable from the natural secretions of the poison glands a 

 series of venins which have all the reactions of the bodies previously 

 considered. Like ricin and abrin, they are not so easily dialyzable as 

 bacterial toxins, and therefore they have also been classed as toxalbu- 

 mins. While up to the present we have not been able to discover the 

 exact chemical composition of any toxin, or even to obtain it in a pure 

 state, many interesting facts upon the nature of toxins have been dis- 

 covered by physiological methods. 



Ehrlich's Theories as to the Nature of Extracellular Toxins. From a 

 large number of most carefully conducted experiments with the toxin 

 and antitoxin of diphtheria, Ehrlich has formulated a theory con- 

 cerning the constitution of the former. This theory has undergone 

 several modifications since it was first proposed, and it is difficult to 

 give an exact statement of it as it now stands. However, we will attempt 

 to state in condensed form its essential points as follows: 



Toxins and antitoxins neutralize one another after the manner of 

 chemical reagents. The chief reasons for this belief lie in the observed 

 facts: (a) that neutralization takes place more rapidly in concentrated 

 than in dilute solutions, and (6) that warmth hastens and cold retards 

 neutralization. From these observations Ehrlich concludes that toxins 

 and antitoxins act as chemical reagents do in the formation of double 

 salts. A molecule of the poison requires an exact and constant quan- 

 tity of the antitoxin in order to produce a neutral or harmless substance. 

 This implies that a specific atomic group in the toxin molecule com- 

 bines with a certain atomic group in the antitoxin molecule. 



The toxins, however, are not simple bodies, but easily split into other 

 substances which differ from one another in the avidity with which they 

 combine with antitoxin. 



