CHAPTER XII. 



INFECTIOUS DISEASES FOR WHICH THE SPECIFIC 

 CAUSE IS NOT DETERMINED. 



§ 341. General consideration. It was not until a 

 comparatively recent date that the nature of the infectious 

 diseases began to be understood. Thej- were, however, differ- 

 entiated in so far as that could be done by clinical evidence 

 alone. With the work of Pasteur, overthrowing the "spon- 

 taneous generation" theory; the introduction of the aniline 

 dyes by Weigert in 1877 : the discovery of solid culture media 

 by Koch in 1881 ; together with the finding of the specific 

 causes of anthrax, Asiatic cholera, tuberculosis and other dis- 

 eases, there naturally came new methods for the study of the 

 etiology of these affections. By the use of newer methods 

 and better instruments of precision and the closer study of. 

 these affections the cause of one after another of the infectious 

 diseases was revealed until the etiology of a large number of 

 them has been made known. These have already been grouped 

 and studied. There are remaining still a number of well 

 recognized diseases for which a specific cause has not been 

 found. The methods for the investigation of the cause of dis- 

 ease that have been effective in case of other diseases have 

 failed here. Until other procedures are devised, the specific 

 causes of these affections will undoubtedly remain undeter- 

 mined. Their study, however, has revealed much concerning 

 their nature, so that measures for their prevention have been 

 found that are quite as effective as they are with those of 

 known etiology. 



RINDERPEST. 



Syno7iynis. Contagious typhus ; steppe murrain ; cattle 

 plague. 



