DIPHTBEBIA. 71 



While crude diphtheria toxin, in the form of sterilized cultures of 

 the bacillus, has been used in securing immunity and in the produc- 

 tion of antitoxin, which has proved to be of such priceless value in 

 the treatment of the disease, no one has up to the present time been 

 able to isolate the poison, and we remain ignorant of its chemical 

 constitution. 



From a large number of most carefully conducted experiments 

 with the toxin and antitoxin of diphtheria, Ehrlich ^ has formulated 

 a theory concerning 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 : ^ 



1. Toxins and antitoxins neutralize one another after the manner 

 of chemical reagents. The chief reasons for this belief lie in the ob- 

 served facts (a) that neutralization takes place more rapidly in con- 

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

 cold retards neutralization. From these observations Ehrlich con- 

 cludes 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 quantity of the antitoxin in order to produce a 

 neutral or harmless substance. This implies that a specific atomic 

 group in the toxin molecule combines with a certain atomic group in 

 the antitoxin molecule. , ^~''' 



2. The antitoxin is a reaction product of the living organism and 

 not a transformation product of the toxin introduced in securing im- 

 munity. It is thought that when the toxin is introduced into the 

 animal body in small quantities it combines with certain side-chains 

 in the molecules of the living cells. These side-chains are supposed 

 to be necessary for the proper functioning of the cells, which, finding 

 themselves deprived in part of their function on account of combi- 

 nation with the toxin, produce other and similar atomic groups or 

 side-chains, and these being formed more rapidly than they are 

 taken up by the toxin, are cast off into the blood and constitute the 

 antitoxin. For instance, when a small quantity of tetanus toxin is 

 introduced into the animal body it combines with certain side-chains 

 in the molecules of the cells of the central nervous system and 

 renders these atomic groups useless so far as the function of the cell 

 is concerned. The cell, in order to compensate for its loss, produces 

 another side-chain similar to the one of which it has been deprived. 

 Being called upon repeatedly to exercise this activity, there is not 

 only compensation, but over-compensation, and the result is that more 

 side-chains are formed than the cell can use, and these break off and 



' Die Wertbemessung des Diphtheriaheilserums und deren theoretische Grand - 

 lagen. 



^For a, more detailed statement of Ehrlich' s theory Bee Chapter VII. 



