134 VETERINARY BACTERIOLOGY 



i. e., an increase in the number of the receptors. The appearance 

 and increase in the freed cell receptors or antitoxins in the blood 

 shows that these receptors are thrown off in large numbers. The 

 antitoxin in the serum unites with the toxin probably in much the 

 same manner as an acid neutralizes an alkali. The principal 

 difference is that in carrying out the test, animal inoculations 

 must take the place of the indicator of the chemist. The union 

 between the toxin and antitoxin has been shown to obey the gen- 

 eral laws of chemical union. 



Constitution of the Toxin. Toxins are easily destroyed by 

 heat, chemicals, light, and air. It will be shown later that the 

 loss of toxicity does not result from a total destruction of the 

 toxin molecule, for it still is able to unite with the antitoxin. 

 It is evident that the toxin molecule is made up of two parts 

 a thermostabile portion, which unites with cell receptors, either 

 in the cell or free as antitoxins, called the haptophore, or binding 

 group, and a thermolabile group, called the toxophore, which causes 

 the cell injury after union by means of the haptophore has taken 

 place. When the toxophore group of a toxin has been destroyed, 

 that which remains is called a toxoid. That toxoids exist may be 

 demonstrated in two ways. The injection of a toxin solution 

 that has been heated to 56 for half an hour into a suitable animal 

 does not result in the development of symptoms of poisoning, but 

 does cause the production of antitoxin; in other words, the toxoids 

 retain the ability to unite with the cell receptors and to bring 

 about their increase and elimination from the cell. An antitoxic 

 serum may be mixed in suitable amounts with a solution of 

 heated toxin (toxoid), and after a time mixed with virulent toxin, 

 and the latter will be found to remain uncombined. The anti- 

 toxin is completely neutralized by the toxoid, and the toxin 

 added subsequently finds no antitoxin free with which it can 

 unite. 



Constitution of Antitoxin. Antitoxin is more stable than the 

 toxin in most cases. However, it is easily destroyed by a tempera- 

 ture of 60 if sufficiently prolonged. There is no reason to sup- 

 pose that it is made up of more than one group. Inasmuch as it 

 has a binding group, this may be called a haptophore. It has not 

 as yet proved possible to separate antitoxins from serum globulins; 



