Protective vaccinations 467 



researches on rinderpest in Cape Colony, extolled Koch's method at 

 the commencement of the epidemic with the object of establishing 

 around the original disease centre an unaffected zone which would 

 interfere with the propagation of the disease. They recognised, 

 however, that this method could not be employed generally, for the 

 reason that it does not set up immunity until the end of eight days, 

 during which period the animals may contract the disease. Further, 

 it demands the sacrifice of a large number of animals in order to 

 provide the vaccinal bile required for the vaccinations ; finally, it 

 confers an immunity of short duration only (four to six months). 



It was necessary, therefore, to find some method that was more 

 generally applicable. With this object Koch himself began to study 

 the blood serum of animals that had recovered spontaneously from 

 rinderpest. He was able to assure not only himself, but several other 

 observers, that this serum was capable of rendering normal animals 

 into which it is injected refractory. Bordet and Danysz, who studied 

 rinderpest in the Transvaal in 1897, made many experiments in this 

 direction and devised a method which gave good results in practice. 

 But it was left to Kolle and Turner to work out a method at once 

 simple and easily applied, one which soon came into general use. 

 This method is known by the name of " simultaneous vaccinations/' 

 It consists in the injection of a protective serum simultaneously with 

 the virulent blood. To prepare the former the authors just men- 

 tioned made use of animals that had recovered spontaneously from 

 rinderpest or of Bovidae that had been immunised by bile or by some 

 other method. It was recognised that the protective power of the 

 serum of animals that have recovered is very small and cannot confer 

 immunity on normal animals, except when injected in large doses. 

 Kolle and Turner showed that if Bovidae that have recovered spon- 

 taneously are injected with very large quantities of virulent blood 

 coming from animals fatally attacked, the protective power of the 

 serum of the former is markedly increased and a serum is obtained 

 which is active in small doses and which gives good results in prac- 

 tice. This serum may be kept for a long time by the addition of a 

 small quantity of carbolic acid. The immunity conferred by this 

 serum upon normal animals is immediate, but of short duration; it [490] 

 is completed by making a simultaneous injection of virulent blood ; 

 we thus obtain a double immunity, one part immediate, the other per- 

 manent ; to get this result, however, the serum must not be mixed 

 with the virulent blood, for when this is done the immunity conferred 



302 



