THE FILTERABLE MICROBES 395 



exanthematici, which they consider the cause of typhus. 

 Further independent confirmation of their results should be 

 awaited. 



The Virus of Small-pox.^ — The virus of this disease was shown 

 to be filterable by Casagrandi in 1908. The vaccine virus, which 

 is generally considered to be the same organism, had been pre- 

 viously filtered . The organism passes through the coarser Cham- 

 berland filters. The virus resists drying for several weeks and 

 remains active in glycerine for eight months, but is quickly ren- 

 dered inert by bile and by sodium oleate. It is also destroyed by 

 heating at 58° C. for 15 minutes. Cell inclusions, which were 

 described by Guarnieri in 1892, are considered by some to repre- 

 sent forms of the pathogenic agent. 



SmaU-pox is an acute disease of man characterized by a general 

 eruption on the skin, at first papular, then vesicular and pustu- 

 lar. It is highly contagious by direct association and by fomites 

 and is readily transmitted by placing bits of crust from dried 

 pustules on the nasal mucous membrane or on a scratch in the 

 skin. Cow-pox is a milder disease which occurs naturally in cows, 

 and has also been produced by inoculating calves with small-pox 

 virus. An attack of either small-pox or cow-pox is followed by 

 immunity to both diseases. Cow-pox in man is a comparatively 

 mild disease. Inoculation results in the formation of a single 

 pustule, rarely surrounded by secondary vesicles, with slight illness 

 for a few days. Edward Jenner in 1798 discovered that cow-pox 

 resulting from artificial inoculation(vaccination) confers an immu- 

 nity to small-pox. Vaccination is now very generally practised 

 in enlightened communities and in such places small-pox is practi- 

 cally unknown. The inoculation is best done by making a very 

 slight superficial linear incision, about 5 mm. long, in the epi- 

 dermis and rubbing into it the vaccine virus. The whole pro- 

 cedure should result in only *a, faint tinge of blood.. When the 

 vesicle appears it should be carefully protected from violence. 

 A normal vaccination causes little inconvenience and is usually 

 completely healed in about 4 weeks after inoculation. Failure 



