66 VACCINE AND SEEUM THERAPY 



immunising power when injected into other suscep- 

 tible animals. Practical methods of immunisation 

 were developed through the work of Dorset, McBryde, 

 and Niles of America. The method devised by them 

 is as follows : It is necessary to start with an animal 

 that has recovered from the disease or has been 

 already immunised. This animal is hyperimmunised 

 by the repeated injections of virulent blood. Such 

 blood must be of a strain of known virulence, estab- 

 lished by tests. This hyperimmunised animal is 

 then bled, the blood defibrinated and preserved by the 

 addition of | to 1 per cent, carbolic acid. This serum 

 should be capable of protecting an animal, in doses 

 of 15 c.c, against an injection of 1 to 2 c.c. of virulent 

 blood. 



The best results, however, have been obtained by 

 the serum simultaneous method. Here a dose of 

 virulent blood — 1 to 2 c.c. — is given together with 

 20 c.c. of serum. At the present time there are 

 numerous American firms which supply standard 

 virulent hog cholera virus, together with the immune 

 serum. This does away with the disadvantages w^hich 

 were associated with the use of virulent blood, as the 

 blood did not always contain the same degree of 

 virulence ; furthermore, it is much more practicable. 

 The serum simultaneous method of vaccination 

 results in the development of an active immunity, 

 which lasts from six to twelve months, or perhaps 

 longer. 



In this country the mortality from swine fever runs 



