SPECIFIC MICRO-ORGANISMS 



tagious 1 but is transmitted from man to man by body lice (Pedi- 

 culus vestimenti). Immunity follows recovery. 



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. 



Small-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 



1 Wilder: Journ. Infect. Dis., 1911, Vol. IX, p. 9. Ricketts and Wilder :Joiirn. 

 A. M. A., 1910, Vol. LV, pp. 309-311. 



