CHAPTER LXIV. 

 THE FILTKABLE VIRUSES. 



Introduction. 



Section I. The virus of Pleuro-pneumonia in cattle, p. 836. 

 Section II. The virus of Foot and Mouth disease, p. 838. 

 Section III. The virus of Horse-sickness, p. 838. 

 Section IV. The virus of Rinderpest, p. 839. 

 Section V. The virus of Bird-plague, p. 839. 

 Section VI. The virus of Sheep-pox, p. 839. 

 " The infectious epithelioses," p. 840. 

 Section VII. The virus of Cow-pox p. 840. 

 Section VIII. The virus of Yellow fever, p. 841. 

 Section IX. The virus of Rabies, p. 841. 

 Section X. Filtrable viruses in the Pasteurelloses, p. 842. 

 Section XI. The virus of Swine fever, p. 843. 

 Section XII. The virus of Acute anterior poliomyelitis, p. 844. 

 Section XIII. The virus of Typhus fever, p. 847. 



PASTEUR put forward the opinion that some micro-organisms were so small 

 as to escape the ordinary method of microscopical investigation ; recent 

 research has proved the truth of this hypothesis, and has shown moreover 

 that micro-organisms too small to be seen with the microscope are respon- 

 sible for a number of diseases. The use of dark-ground illumination has 

 not hitherto given any interesting results in this connexion. 



It is characteristic of the filtrable viruses that they can pass through 

 certain porous porcelain or similar niters and for this reason they are some- 

 times known as " filter passers." 



To demonstrate this property too fine a filter must not be used : a Berke- 

 feld V or Chamberland F are the most suitable for the purpose though occa- 

 sionally a more porous bougie is employed (Chamberland Fj to F 10 made to 

 the instructions of Borel, or Berkefeld V worn down on a grindstone or with 

 a glass cutter). 



The virus is prepared as follows : Dilute the infected material (defibrinated 

 blood, serous exudate, emulsion of internal organs, etc.) with water in which 

 a culture of an easily-recognized micro-organism preferably a motile organism 

 has been emulsified : this organism acts as a control. Filter the emulsion 

 under a low pressure. On cultivation the filtrate should yield no visible 

 growth but on inoculation into a susceptible animal should give rise to the 

 original disease. 



In experiments with ultra-microscopic viruses certain conditions must be strictly 

 observed. The filter should be new and must be sterilized before use : the process 

 of filtration should occupy not more than about 2 hours : the pressure applied 



