58 CLINICAL BACTERIOLOGY AND 



them side-chains or receptors. A side-chain attached to a 

 cell may join to itself a particle of oxygen, fat, carbo- 

 hydrate, etc., and so take part in the nourishment of the 

 cell. In the same manner it may unite with a molecule of 

 poison, such as a toxin. Now, this toxin, through the 

 medium of the side-chain, becomes part of the cell, 

 and if strong enough will poison it and actually produce 

 death of the cell itself ; or it may cause death only of the 

 side-chain, in which case the latter would be thrown off 

 and a new one formed by the cell. Following upon the 

 destruction of the side-chain, several more chains are 

 produced to take its place, with the result that the cell 

 cannot retain them all, and they consequently become 

 detached and are cast off into the lymph around the cell, 

 and eventually reach the blood-stream, constituting free 

 side-chains, whose function now appears to be to unite with 

 the molecules of the toxin before it reaches the cell. In 

 this manner these free side-chains show antitoxin properties 

 which prevent the action of the poison upon the cells, 

 giving thereby to the patient an immunity. Further, if the 

 serum containing these free side-chains is injected into 

 another animal, they will confer upon that animal the same 

 degree of immunity as was possessed by the original 

 immunized animal, which explains the prophylactic and 

 curative action of antitoxin. 



Toxins are easily destroyed by heat, chemicals, and light, 

 but the loss of toxicity does not result from a complete 

 destruction of the toxin molecule, for it is still able to 

 unite with the antitoxin. It is clear, then, that the toxin 

 molecule is made up of two parts : a thermostable portion, 

 which is capable of uniting with cell receptors either in the 

 cell itself or free as antitoxin, and called the haptophore ; 

 and a thermolabile group, which causes the cell injury after 

 union by means of the haptophore has taken place, and 

 called the toxophore. When the toxophore group of a 

 toxin has been destroyed, that which remains is called the 

 toxoid. 



