122 IMMUNITY AND INFECTION 



or haptophore group, and a poisoning or toxophore group. The former 

 is relatively thermostabile, the latter thermolabile. If toxin is heated 

 to 70 C. for a few minutes, or allowed to stand for several weeks, it 

 will be found that the poisonous property of the toxin has disappeared, 

 or has been materially reduced. It still retains its original powder of 

 uniting with and neutralizing antitoxin, however. The thermolabile 

 toxophore group has been destroyed or weakened by the heating 

 process, or on standing. The thermostabile group the haptophore 

 group has not been impaired. Toxin which has lost part or all of 

 its original poisoning properties, but which still unites with antitoxin 

 is called toxoid. 



The soluble toxins of the diphtheria and tetanus bacilli are not 

 simple substances; they contain at least two physiologically separate 

 poisons. Thus, the toxin of the diphtheria bacillus contains in addi- 

 tion to the poison which produces acute symptoms, a second poison 

 which acts slowly and appears to be responsible for postdiphtheritic 

 paralyses and emaciation. This second poison has less affinity for 

 antitoxin than the acute poison, and it is called a toxone. Similarly, 

 the tetanus toxin appears to consist of at least two distinct poisons 

 tetanospasmin, which has an especial affinity for nerve cells and 

 which elicits the acute symptoms of tetanus, and tetanolysin, which 

 causes hemolysis of erythrocytes. The injection of soluble or exo- 

 toxins produced by bacteria leads to the formation of soluble specific 

 antibodies which are called antitoxins. Antitoxins are supernumerary 

 side-chains which have been produced in excess of the physiological 

 needs of the cell, in response to the stimulus of a specific toxin, and 

 cast off into the blood stream. 



It has been shown that repeated injections of solutions containing 

 active enzymes as, for example, rennin into animals, is followed 

 by the appearance in the blood stream of specific antibodies which 

 will prevent the activity of the homologous enzyme. These anti- 

 bodies, or anti-enzymes, as they are called, exhibit the specificity and 

 other characteristics which distinguish antitoxins. 



Antitoxins and anti-enzymes are called side-chains of the first 

 order by Ehrlich. They possess the property of combining with and 

 neutralizing their respective toxins or enzymes. 



Side-chains of the Second Order. If substances of greater com- 

 plexity than those just described are needed for the nutrition of the 

 cell, some preliminary treatment, probably in the nature of digestion, 

 may be required to prepare these substances for assimilation after 



