24 GROUPING OF INFECTIOUS DISEASES 



various specific maladies that the lesions in a given disease 

 vary in different species and in individuals of the same species 

 to a marked degree. This fact precludes the possibility of 

 classifying or arranging them after their morbid anatomy, if 

 the idea of a specific etiology is to be adhered to. If the infec- 

 tious diseases are to be considered as parasitisms, as they ap- 

 pear to be, the only logical method of classifying them accord- 

 ing to the writer's opinion, is the one suggested by their eti- 

 ology, namel}', that they shall be placed in groups according 

 to their cause. Thus a single lesion found in the glands of 

 the head, in the lungs, in the liver, in the mesenteric glands, 

 in the skin, in the joints, or in the generative organs would be 

 called tubercular if the bacteria of tuberculosis could be demon- 

 strated to be its cause. The same conclusion would be main- 

 tained regardless of the character of the lesion, whether cel- 

 lular, purulent, caseous or calcareous. These facts are enough 

 to suggest that the most direct method of arranging these dis- 

 eases for purposes of .study is in groups composed of like gen- 

 eric etiological factors. 



Most of the known specific causes of the infectious dis- 

 eases of animals are bacteria. It is necessary, therefore, to 

 choose from among the numerous classifications one to be fol- 

 lowed in grouping the diseases according to the genera of bac- 

 teria producing them. Of the various systems, the one by 

 Migula seems to be the simplest and most natural and conse- 

 quently it is selected. The onl}^ radical difference between it 

 and the others, so far as pathology is concerned, rests in the 

 fact that the old genus Baderhivi is revived, but with a new 

 meaning. All rod-shaped, non-motile bacteria are placed in 

 this genus. This causes a change of the generic name from 

 Bacillus to Bacterium of a number of pathogenic bacteria such 

 as those of tuberculosis, anthrax, swine plague and others of less 

 importance. 



Following the bacterial diseases are placed those caused 

 by higher fungi.* After the fungous diseases are placed those 



*The number of diseases included in this work that are caused by 

 fungi, protozoa and higher animal parasites are so few that they have 

 been grouped under these more general headings rather than separated 

 into groups of the same generic origin. 



