PROPHYLACTIC IMMUNIZATION OR VACCINATION 671 



which can be carefully controlled and tested, any danger of transmitting 

 syphilis being thus obviated, because the heifer or cow used in the pre- 

 paration of the virus is not subject to this disease. The opponents to 

 vaccination, however, persist in using old and obsolete statistics regard- 

 ing the transmission of syphilis to support their claims, although these 

 have absolutely no bearing upon the modern methods of preparing the 

 virus. 



Seed Virus. This refers to the virus for vaccinating the calves or 

 other animals used, and is a most troublesome factor to those engaged 

 in this work. According to Park and Huddleston, a sufficient amount of 

 vaccine virus should be on hand to vaccinate from 40 to 50 persons. 

 Five children in good health and not previously vaccinated should then 

 receive an inoculation, each spot being of the size of a ten-cent piece. 

 On the fifth day after vaccination the upper layer of the resulting vesicle 

 should be removed, and sterilized bone slips be rubbed on the base thus 

 exposed. From 100 to 200 slips on each side of the slip may be charged 

 from each child. The slips should be allowed to dry for a minute, and 

 should then be placed in a sterilized box and preserved in cold storage, 

 where they will remain active for at least two or three weeks. The 

 aforenamed observers now use rabbits alternately to obtain seed virus. 



Subsequent animals are vaccinated with any one of three vaccines 

 (1) Slips charged from typical vesicles of a calf; (2) slips charged with 

 the serum from a calf after removal of the vesicles; (3) the glycerinated 

 virus may be used to vaccinate succeeding calves, but in this case it is 

 necessary to keep the glycerinated virus for two or three months, since 

 the use of fresh virus on a succession of calves leads to prompt degenera- 

 tion of the vaccine and to the production of infected vesicles. 



The New York Vaccine Laboratory produces a virus that is never 

 more than four successive transfers from a human case of vaccinia, 

 and is guaranteed to give 100 per cent, of "takes" in primary vaccina- 

 tion. 



Animals. Various animals have been used, but female calves from 

 two to four months of age are preferable. Older animals may be used, 

 and in several European institutes cows are usually employed. With 

 properly constructed operating-tables, they may be handled with 

 comparative ease. Rabbits have also been used, especially in pro- 

 pagating the seed virus and to obtain pure and highly active viruses. 



The calves are kept under supervision for at least a few days. In 

 some institutes they are tested with tuberculin, although with good 

 veterinary inspection this test is not necessary. Soon after admission 



