South African Horse Sickness, etc. 567 



Koch, experimenting later, found a great difference iu the 

 virulence of the blood of successive sick animals, so that with 

 each new animal furnishing the virus the dose must be carefully- 

 determined by experiment before it can be safely used for im- 

 munization. The following gives, not a safe dose for every case 

 but an approximation to the average doses, to be tested in the 

 , case of each animal furnishing the virulent blood : 



The virulent blood is drawn by cannula from the jugular of a 

 pronounced case of the disease.. It is defibrinated, strained 

 through wet, sterilized muslin, then mixed with an equal amount 

 each of sterile glycerine and sterilized water having an admixture 

 of I part of carbolic acid to every 1000, and finally placed in 

 bottles, well filled, stoppered and preserved in an ice chest, in 

 the dark for 2 or 3 weeks. The globules are dissolved and their 

 solids should be separated by a second filtration through wet 

 sterilized muslin. The liquid is preserved in sterilized bottles, 

 well filled, and stoppered and kept in an ice chest. For inocula- 

 tion the required dose is diluted in enough sterilized sodium 

 chloride solution (0.85 per cent.) to makescc. The injection is 

 made beneath the skin of the neck high enough up to allow of 

 the injection of the immunizing serum below it, 4 days later. 



To prepare the immunizing serum a recovered horse is given 

 intravenously, 2 quarts of the warm, fresh, defibrinated blood of 

 an animal in the last stages of horsesickness, the blood having 

 been first passed through a sterilized wet muslin filter. Four 

 such injections are given at intervals of not less than 14 days. 

 Fourteen days after the last injection 4 or 5 quarts may be drawn 

 and used for immunizing serum, and the same amount on four 

 siiccessive occasions at intervals of 7 days. After some months 

 rest the horse may be again fortified and its serum used anew. 



