VARIOLA AND VARICELLA 553 



variola on the calf have failed. In the successful cases 

 the lymph obtained from the calf has, on inoculation upon 

 children, produced typical vaccinia without any untoward 

 results. The positive results obtained by the inoculation 

 of variolous material being so few, a doubt arises whether 

 in these cases there may not have been some fallacy, such 

 as accidental contamination with vaccinia. Simpson, 

 however, performed his experiments within the precincts 

 of a smallpox hospital and away from possible vaccine 

 infection, and Copeman * found that variola may be readily 

 inoculated upon monkeys, and after several passages 

 through these animals is easily inoculable upon the calf. 

 He suggests, therefore, that vaccinia in the calf was origin- 

 ally due to infection with inoculated smallpox, so prevalent 

 at the time of Jenner's discovery. A somewhat parallel 

 instance of the attenuation of a virus by passage through 

 another animal is recorded by Sticker and Marx in the 

 case of birdpox, which produces an extensive smallpox- 

 like eruption in fowls and pigeons. In fowls and in pigeons 

 the virus retains its pathogenic properties for each bird 

 unaltered for any number of inoculations, but the pigeon 

 strain, after a few inoculations into fowls, completely loses 

 its virulence for the pigeon. There seems little doubt, 

 therefore, that vaccinia is modified variola, and the rationale 

 of vaccination rests upon a scientific basis. 



The preparation of vaccine lymph is fully described by Blaxall. 2 

 Calves are vaccinated with lymph under aseptic precautions, and 

 five days later the contents of the vesicles are scraped off, the pulp 

 is triturated in a machine, and is then placed in six times its weight 

 of sterilised 50 per cent, pure glycerin in distilled water, and stored 

 for about a month in test-tubes, until agar cultivations show that 

 extraneous bacteria have died out, when it is issued for use. It 

 remains very active for fifty to sixty days, after which it begins to 

 deteriorate. 



1 Brit. Med. Journ., 1901, vol. i, p. 1134, and 1901, vol. ii, p. 1736. 



2 Rep. Med. Off. Loc. Gov. Board for 1898-99, p. 35. 



