112 INFECTION 



radical. Each of the side or lateral arms is composed of two portions 

 one, the haptophore group, which has a chemical affinity for certain 

 chemical constituents of the tissues of susceptible animals, and the other, 

 the injury-producing portion, called the toxophore group. (See Fig. 40.) 

 An animal is susceptible to a toxin only when its cells contain substances 

 that possess a chemical affinity for the haptophore group of the toxin, 

 and also substances susceptible to the toxic action of the toxophore group. 



The toxophore group is far more unstable and susceptible to dele- 

 terious influences than is the haptophore portion. When the molecule 

 has lost the toxophore radical, it is known as a toxoid, which is still 

 capable of uniting with the side arms of cells but is devoid of toxic action. 



Nature of Toxins. It has been abundantly demonstrated that 

 toxins are colloids, and in many respects bear a close resemblance to 

 enzymes. (See p. 254.) The toxins are synthetic products of bacterial 

 activity. They are of absolutely specific nature, and in this manner 

 differ frorn ptomains, which are cleavage products from the medium 

 upon which the bacteria have been grown. Furthermore, ptomains of 

 similar properties may be produced by several different kinds of bacteria, 

 and accordingly are non-specific in nature. Toxins, like ferments, can 

 give rise to antibodies, whereas ptomains cannot produce them. 



The extracellular or soluble toxins differ from the intracellular toxins 

 in that they are more easily diffused throughout the animal juices, and 

 that their diffusion occurs independently of the invasiveness of the 

 bacteria, so that comparatively few microorganisms growing at some 

 unimportant focus, and causing but slight local lesions, may be able to 

 give rise to profound general intoxication. This is well illustrated in 

 diphtheria, where the local lesion in the throat may be quite small, 

 and in tetanus, where it may indeed be undiscoverable yet either, 

 through the action of their toxins on special tissues, may cause Drofound 

 intoxication and death. 



Selective Action of Toxins. Extensive studies of the toxins of 

 diphtheria and tetanus and of cobra venom have shown that they are 

 quite complex, and are usually composed of two or more distinct and 

 separate toxins possessing different pathogenic properties, although one 

 of these may predominate in producing symptoms. 



All infections with the group of true toxin-producing bacteria mani- 

 fest certain non-specific symptoms of general intoxication, namely, 

 fever, headache, malaise, prostration, etc.; but the typical symptoms 

 of these diseases are due to the remarkable selective action of the toxins 

 upon certain cells or organs, dependent upon the ability, chemical, 

 physical, or both, of the toxin to combine with these specific cells. For 



