674 ACTIVE IMMUNIZATION 



According to Park and Huddleson, 10 grams of pulp and 200 charged 

 slips would be an average yield from a calf, and when made up should 

 suffice to vaccinate at least 1500 persons. Calves vary greatly in their 

 yield of virus. Of two calves vaccinated in exactly the same manner, 

 one may furnish material for 500 vaccinations and the other for 10,000 

 inoculations. 



Testing the Vaccine. The virus may be tested for its efficacy by a 

 variety of methods. Calmette and Guerin * inoculate rabbits upon the 

 inner surfaces of the ears and estimate the potency of the virus from the 

 speed of development and the size of the resulting lesions. Guerin 2 

 estimates the potency of virus quantitatively by inoculating rabbits 

 with serial dilutions ranging from 1 : 10 to 1 : 100. Fully potent virus 

 should cause closely approximated vesicles in a dilution of 1 : 500, and 

 numerous isolated vesicles in a dilution as high as 1 : 1000. 



Quantitative estimation of the bacteria in the glycerinated virus 

 is made by the plating method, and the vaccine used only when the 

 numbers of bacteria have been greatly diminished or are entirely absent. 

 The vaccine is also tested for tetanus by injecting relatively large 

 quantities subcutaneously into guinea-pigs and mice. 



Under the Federal Law of July 1, 1902, and the regulations framed 

 thereunder, all firms manufacturing vaccine virus are required by the 

 Secretary of the Treasury to obtain a license before they may sell their 

 products in interstate commerce. The vaccine laboratories are care- 

 fully inspected by an official of the, Hygienic Laboratory of the United 

 States Public Health and Marine-Hospital Service; the inspector 

 carries away with him as many samples of virus as he wishes, and addi- 

 tional samples are purchased in the open market in different parts of the 

 country. All these are subjected to a vigorous bacteriologic examina- 

 tion, especially for tetanus bacilli, by a laboratory worker who devotes 

 all his time to this work. The federal regulations require each vaccine 

 institute to .perform a careful autopsy on each calf after the vaccine 

 virus has been removed, and if any communicable disease is found or 

 suspected in the animal, the virus must not be placed on the market, 

 but must be destroyed. In accordance with this law, permanent records 

 of the bacteriologic examinations of the virus and of the autopsy shall 

 be kept in each institute. 



Noguchi's Method of Preparing Cowpox Virus. Noguchi 3 has suc- 

 ceeded in freeing vaccine virus from all associated bacteria by means of 

 1 Ann. de 1'Inst, Pasteur, 1902. 2 Ann. de 1'Inst. Pasteur, 1905. 



8 Jour. Exper. Med., 1915, 21, 539. 



