SECTION IV 



DISEASES CAUSED BY FILTRABLE VIRUS, THE EXANTHE- 

 MATA, AND DISEASES OF UNCERTAIN ETIOLOGY 



CHAPTER XLV 



GENERAL CONSIDERATION OF FILTRABLE VIRUS, SMALLPOX AND 



RABIES 



FILTRABLE VIRUS 



RECENT investigations into the causation of disease have revealed 

 that a considerable number of infections may be caused by organisms 

 too small to be held back by niters through which even the smallest 

 bacteria cannot pass. The earliest observations of such "filtrable 

 virus" are probably those of Frosch (1898) in foot-and-mouth dis- 

 ease and of Beijerinck in the mosaic disease of tobacco. Since then 

 similar investigations have shown that a large number of diseases 

 are probably caused by such minute organisms; their investigation, 

 loDg delayed by the belief in their invisibility by even the most 

 powerful microscopic aid, and by our inability to cultivate them, 

 has taken new impetus from the discovery and probable cultivation 

 of minute globoid bodies from the virus of poliomyelitis by Flexner 

 and Noguchi (see below). 



Similar bodies have since then been seen in connection with 

 other diseases by many observers, and in lethargic encephalitis 

 recently Strauss and Loewe claim to have cultivated organisms quite 

 similar to those of poliomyelitis cultivated by Noguchi. In thinking 

 of filtrability, however, one must remember that filtrability, like 

 diffusibility, is not an absolute concept, and that much depends 

 upon the nature of the filter used and the amount of suction applied. 

 Thus, there has been much discussion as to the filtrability of diseases 

 like syphilis, yellow fever, etc., and in conditions caused by flexible 



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