898 DISEASES CAUSED BY FILTRABLE VIRUS 



Beginning with a mixture containing equal weights of glycerin and 

 vaccine pulp, dilutions are made with sterile water ranging from 

 1 in 10 to 1 in 100. Rabbits are shaved over the skin of the back 

 and 1 c.c. of each of these dilutions is rubbed into the shaved areas. 

 Fully potent virus should cause closely approximated vesicles in a 

 dilution of 1 in 500, and numerous isolated vesicles in a dilution 

 as high as 1 in 1,000. 



Quantitative estimations of the bacteria in the glycerinated virus 

 should be made by the plating method and the vaccine used only 

 when after several weeks of preservation the numbers of the bacteria 

 have been greatly diminished. In glycerinated pulp the bacteria 

 will often disappear entirely in the course of a month. The vaccine 

 should also be tested for the possible presence of tetanus bacilli, by 

 the inoculation of white mice. 



Vaccination of human beings is performed by slightly scarifying 

 the skin of the arm or leg with a sharp sterile needle or lancet and 

 rubbing into the lesion potent vaccine virus. The virus was formerly 

 dried upon wood, bone, or ivory slips and moistened with sterile 

 water before the operation. At the present day the glycerinated 

 pulp is almost universally employed. 



Since the ordinary scarification method has not been universally 

 satisfactory, other methods of vaccination have been suggested. 

 Occasional failure of the scarification method may in part be due 

 to the fact that the glycerinated, ripened virus as used in most 

 countries, has lost considerably in potency. We have seen men in 

 the American Army successfully vaccinated with French virus after 

 two vaccinations with American virus had failed. The French virus 

 used had not been allowed to ripen in glycerine, was reasonably 

 fresh (so-called green virus) and was, therefore, probably more 

 potent. The fact that it still contained staphylococci and other 

 organisms did not in these cases lead to infections of any importance. 

 It must, however, always be dangerous, and the use of green virus, 

 while perhaps more efficient from the point of view of vaccination, 

 does not seem to us to be commendable. It is probably better to 

 attempt modification of the present method by a more efficient in- 

 troduction of the virus. The alternative methods which have been 

 suggested are puncture in which drops of virus are placed on the 

 skin and punctures made through the drops. Scarification or small 

 incisions through the drops have also been recommended. Recent 



