THE FILTERABLE VIRUSES 197 



THE FILTERABLE VIRUSES. 



Some diseases are produced by organisms so minute 

 that they will pass through the pores of a kieselguhr or 

 porcelain filter, and remain invisible under the microscope 

 (ultra-microscopic organisms). In some cases, the organ- 

 isms are only ultra-microscopic and filterable at one stage, 

 the filtered virus producing organisms more or less well 

 within the limits of visibility. 



Some filterable organisms (those of rabies, variola, 

 vaccinia, and anterior poliomyelitis, for instance) will 

 live in glycerin for weeks without losing their virulence. 

 According to Cockayne (Medical Press, February 12, 

 1913), some are readily destroyed by weak antiseptics 

 such as 2 per cent, phenol, menthol, or hydrogen per- 

 oxide. Some resist very low temperature: 2 C. to 

 - 12 C. Many are readily killed by exposure to 50 to 

 65 C. for a few minutes. With the exception of the virus 

 of cattle pleuro-pneumonia and the possible exceptions 

 of those of infantile paralysis and typhus, none has been 

 cultured on artificial media (see also Twort, Lancet, 

 December 4, 1915). 



Cockayne (loc. cil.) says: ' In those filterable organisms 

 which can only pass through a kieselguhr filter, and are 

 therefore visible under the microscope, there is a resem- 

 blance in staining reactions so far as these have been 

 carried out. They stain well with Loffler's methylene 

 blue, less well with haematoxylin, and there is round them 

 a clear halo an appearance altogether different from that 

 obtained by controls of crushed liver pulp passed through 

 a similar filter.' 



Pleuro-pneumonia in cattle is characterised by the 

 peculiar marbled appearance of the lungs, accompanied 

 by great distension of the connective tissue, with a yellow- 

 ish albuminous fluid. The serious symptoms are due to 

 toxins, and death frequently ensues. Roux and Nocard 

 describe a minute refractile body just visible with the 

 highest and best powers, but small enough to pass 

 through the pores of a Berkefeld filter. It was found 

 to stain with gentian violet, methyl violet, and hot carbol 

 fuchsin, though never more than half the particles took 

 up the stain. 



