SMALLPOX AND VACCINIA 573 



2. Virus obtained from animals which have been inoculated with 

 lymph from human vaccine pustules, either directly or indirectly, 

 through a series of calves this is known as retro vaccine. 



3. Vaccine obtained by passing smallpox virus through the cow 

 the so-called variola vaccine. 



Preparation of Vaccine Virus. Healthy female calves about three 

 months of age are selected. After thorough cleansing the animal is 

 fastened upon an operating table of special design and the abdomen 

 and inner aspect of the thighs are shaved. If disinfectants have been 

 used they are removed with sterile water. Shallow parallel incisions 

 about half an inch apart and just deep enough to become slightly 

 reddened .are made, and the vaccine is thoroughly rubbed into the 

 scarified area. The quarters in which inoculated calves are kept are 

 scrupulously clean; the animals are preferably fed an exclusive milk 

 diet. Dust is reduced to a minimum and excreta are promptly removed 

 by flushing with a stream of water. 



Four to six days after inoculation, depending upon the rate of 

 development of the vaccine vesicles, the calf is again placed upon 

 the table, the vaccinated area washed with sterile water and then 

 rubbed gently with sterile absorbent cotton; any crusts or scabs are 

 removed. The slightly elevated confluent eruption is curetted away 

 and appears as a pulpy mass, which is thoroughly ground in a mill 

 of special design with three or four times its volume of 60 per cent. 

 glycerin. 1 The ground and comminuted glycerized virus thus pre- 

 pared contains variable numbers of bacteria; 2 as many as 700,000 

 per c.c. have been found. 3 Of the more common microorganisms, 

 various molds, yeasts and members of the coccal group are usually 

 present. Very rarely cases of tetanus have been reported following 

 vaccination. 4 The extreme rarity of these cases and the possibility 

 of infection from uncleanly conditions after the vaccination was 

 made make it doubtful that vaccine may be a vehicle for the trans- 

 mission of tetanus. 5 



The addition of the glycerin to the pulp obtained from vaccinated 

 calves plays an important part in reducing the number of bacteria 



1 Carbolic acid (1 per cent.) is frequently added to the glycerin before mixing it with 

 the pulp; experience indicates that the carbolized vaccine virus loses its potency more 

 rapidly than when glycerin alone is used. 



2 See Rosenau, Am. Med., 1902, iii, 637, for Bacteriology. 



3 Theobald Smith, loc. cit. 



4 Wilson, Jour. Am. Med. Assn., 1902, xxxviii, 1147, 1222. McFarland, Jour. Med. 

 Research, 1902, vii, 474. 



' 5 See Francis, Bull. No. 95, U. S. P. H. and Marine Hosp. Service, 1914, for results of 

 implanting tetanus spores directly into vaccine. 



