CHAPTER XXIX. 



FILTERABLE VIRUSES, DISEASES OF UNKNOWN 

 ETIOLOGY. 



FILTERABLE VIRUSES. 



Acute Anterior Poliomyelitis. Epi- 

 demic Poliomyelitis. 



Typhus Fever (Tabardillo, Brill's 

 Disease). 



Yellow Fever. 



Foot and Mouth Disease. 



Contagious Pleuropneumoniaof Cattle. 



DISEASES OF UNKNOWN ETIOLOGY. 

 Measles. 

 Scarlet Fever. 

 Rabies. 

 Trachoma. 



Smallpox (Variola) and Vaccinia. 

 Dengue. 



Rocky Mountain Spotted Fever. 

 Mumps. 



FILTERABLE VIRUSES. 1 



THE viruses of certain diseases of plants, animals and of man are 

 fully virulent after they have been passed, suspended in fluid, through 

 filters of unglazed porcelain or diatomaceous earth of definite degrees 

 of fineness. These filters will not permit the passage of organisms 

 as minute as Micrococcus melitensis, but Wherry 2 has shown that 

 the bacillus of guinea-pig pneumonia, an actively motile bacillus 0.3 

 to 0.5 micron in diameter and 0.7 micron in length, will also pass 

 through such filters unharmed. 



The restraining action of filters of unglazed porcelain and diato- 

 maceous earth appears to depend rather upon the tortuous passages 

 in the walls of the filter than upon the ultimate minuteness of these 

 channels. This possibility is suggested by experiments using filters 

 of theoretically equal degrees of fineness of material, but of varying 

 thickness; it has been shown that bacteria may be forced ' through 

 the thinner walled filter, but not through the thicker. Longer bacteria, 

 Bacillus typhosus for example, will pass through filters, provided time 

 enough for their development is given. The supposition is that the 

 organisms grow around and through tortuous passages which effec- 

 tually hold the bacteria in the channels when pressure is applied. For 

 this reason filtration must not be prolonged much more than an hour, 

 and too much pressure (or suction) must be avoided. 



1 See Wolbach, Jour. Med. Research, 1913, xxvii, 1, for resume of literature. 



2 Jour. Med. Research, 1902, viii, 322. 



