1 8 CLASSIFICATION OF DISEASES 



glands, in the skin, in the joints, or in the generative organs, 

 would be called tubercular if the bacteria of tuberculosis could 

 be demonstrated to be its cause. The same conclusion would 

 be maintained regardless of the character of the lesion, 

 whether cellular, purulent, caseous or calcareous. These facts 

 are enough to suggest that the most direct method of arrang- 

 ing these diseases for purposes of study is in groups composed 

 of like generic etiological factors. 



Most of the known specific causes of the infectious dis- 

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

 carrying out this plan to choose from among the numerous 

 classifications one to be followed in grouping the diseases ac- 

 cording to the genera of bacteria producing them. Of the 

 various systems, the one by Migula seems to be the simplest 

 and most natural and consequently it is selected. The only 

 radical difference between it and the others, so far as pathol- 

 ogy is concerned, rests in the fact that the old genus Bacterium 

 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 Bacilhcs to Bacterium of a number of 

 pathogenic bacteria, such as those of tuberculosis, anthrax, 

 swine plague and others of less importance. 



Because of the few species of fungi and protozoa that 

 are pathogenic for animals, systematic classifications of these 

 organisms are not introduced. For such classifications the 

 student is referred to the various works'^ou mycology for the 

 fungi and the excellent work by Calkins, — " The Protozoa" 

 for the protozoa. In this elementary pathology, all that seems 

 to be necessary concerning the biology and classification of the 

 pathogenic protozoa will be given in connection with genera 

 and species under the " etiology ' ' of the diseases they produce. 



The chapter on diseases caused by fungi naturally fol- 

 lows those on the bacterial diseases. 



§ ID. Migula's classification of bacteria. The genera 

 of the five families are included. 



