310 BACTERIOLOGY FOR NURSES 



obtained directly from healthy animals, the production of which 

 can be carefully controlled and tested. 



The virus used for vaccinating the animals (seed virus) may 

 be prepared in several ways. That usually employed by the New 

 York City Health Department is obtained by first passing an 

 emulsion of crusts obtained from healthy children about nineteen 

 days after vaccination through a calf and subsequently through 

 rabbits. The pulp obtained from the rabbit lesions is emulsified 

 in a solution of glycerin and serves as seed for inoculating calves 

 for the regular supply of vaccine. 



Young female calves from two to four months old that are certi- 

 fied to be free from disease are prepared for vaccination. The 

 posterior abdomen and inner surface of the thighs are shaved, 

 washed with soap and water, then with sterile water and alcohol, 

 and dried with a sterile towel. Over this area a number of long 

 incisions about a quarter of an inch apart are made into which the 

 seed virus is rubbed. 



After vaccination the calves are kept in specially constructed 

 stables with concrete floors and walls; they stand upon raised 

 racks of galvanized iron and are fed upon milk. 



On the fifth day the inoculated area is washed with sterile water 

 and sterile cotton and the crusts are removed. The soft pulpy 

 mass remaining is scraped with a sterile curette into a sterilized 

 container and mixed with four times its weight of glycerin and 

 water (glycerin 50 per cent, water 49 per cent, carbolic acid I per 

 cent). The diluted pulp is passed through a fine meshed sieve, 

 after which it is tested for purity by (1) plating on agar each week 

 for five weeks and counting the colonies (usually by the end of 

 three weeks no growth occurs, the glycerin and carbolic acid hav- 

 ing killed off all the contaminating organisms) ; (2) animal inoc- 

 ulations to test for streptococci and tetanus bacilli. 



After the product has been found to be free from all extraneous 

 organisms its efficiency is tested by inoculating fifteen previously 

 unvaccinated children, all of which must show a perfect " take " 

 in order that the vaccine may be passed as up to standard. After 

 it has been issued for general use a clinical test is made every two 



