PART THREE-SPECIAL. 



CHAPTER XXIV. 



Although a consistent classification of the infec- 

 tious diseases, on the basis of immunity, is impos- 

 sible at the present time, a certain grouping is de- 

 sirable for the sake of convenience. The following 

 arrangement of those diseases we are able to con- 

 sider is made on a basis which is partly etiologic, 

 partly with reference to the pathogenic properties 

 of the micro-organisms, and partly to the nature 

 of the reactions excited in the body by infection or 

 immunization. In some instances nothing more 

 than general analogies suggest themselves as a 

 basis for the grouping, which is necessarily provi- 

 sional and imperfect. 



GROUP 1. 



Diseases, natural or experimental, which are 

 caused by soluble toxins of bacterial, animal or 

 plant origin. Infection or immunization induces 

 immunity to subsequent attacks (except in hay fe- 

 ver), the immunity being characterized by the 

 formation of serum antitoxins, and occasionally of 

 bacteriolysins and agglutinins. The serums of 

 highly immunized animals are protective and cur- 

 ative for the corresponding intoxications in man 

 and other animals. 



A. BACTERIAL DISEASES. 

 I. DIPHTHERIA. 



Bacillus diphtheria, or the Klebs-Loeffler bacil- 

 lus, was discovered by Klebs in 1883, and more 



