Immunization. 281 



were protected by the serum inoculation will not become affected 

 by the disease later on, or only exceptionally, in spite of the 

 existing dangers of infection. This leads to the belief that the 

 animals which were given a passive immunity by the immune 

 serum, have acquired an active immunity as a result of a natural 

 infection which has taken place in the meantime. 



On the basis of this experience it is advisable to treat all 

 herds which are threatened by the infection with the immune 

 serum, and especially those in which the disease has already 

 appeared, and to retain -the drove in the same place until the 

 infection is eradicated. At the same time the apparently 

 affected animals should be separated, and those which are af- 

 fected severely should be slaughtered. In case the disease 

 appears again in the herd it is advisable to repeat the injection 

 with the immune serum. 



Dorset, McBryde & Niles (1905-1907) treated immune hogs by 

 two methods. In the "quick method" they injected one dose of 900 

 to 1500 cc. of virulent blood (10 cc. per pound of body weight) sub- 

 cutaneously, in the "slow method" gradually increasing doses of 500 

 to 900 cc. (1 to 5 cc. per pound of body weight) of such blood at 

 intervals of 3 to 4 weeks or even longer periods. About three weeks 

 after the single injections, or after the last injection, as well as later at 

 various intervals, they have drawn blood from the injected animals. 

 The serum from such blood when obtained by defibrinating, or by allow- 

 ing it to stand immunized animals weighing from 25 to 50 pounds when 

 injected in 20 cc. doses, against a simultaneous infection of 1 to 2 g. 

 of virulent blood, and also against subsequent natural exposures. 



Later the forced immunization was accomplished by injecting the hogs once 

 or twice intravenously with 5 cc. of virulent blood per pound of body weight, or 

 with 10 cc. intraperitoneally by a single injection. 



The immune serum is used in the United States mostly for' simultaneous 

 inoculations (see below), and is only rarely employed alone. Experiments regard- 

 ing the curative action of the serum showed that if the serum treatment is under- 

 taken not later than four days after infection, the outbreak of the disease may 

 be prevented. According to the reports of the Bureau of Animal Industry the 

 results from the practical application of the serum are very satisfactory. 



Uhlenhuth and his co-workers (1907) produced a similarly potent 

 serum from hogs, to which they had given several subcutaneous injec- 

 tions 6i 25 to 100 ce. of virulent material, mostly blood. The serum 

 in doses of 10 to 50 cc. protected healthy pigs from a subsequent 

 severe, natural infection, while animals which were not inoculated, 

 ' or which were given large doses of horse serum, died from hog cholera. 

 Doses of 10 to 20 ce. also protected against the pathogenic effects of 

 0.5 cc. of virulent blood, when injected subeutaneously at the same 

 time. Potent serum can be prepared only from hogs, not from horses 

 or asses. 



Practical experiments with immune serum have been made in various herds, 

 most of which were severely affected, 330 out of 743 hogs being immunized while 

 413 were not given the treatment. The loss among the^ inoculated hogs was 61 

 (18.4%), among those which were not inoculated 212 (51.3%). The dose of the 

 serum was 20 to 50 ce. 



Ostertag's laboratory experiments with serum of successively 

 highly immunized hogs have also given good results. With this serum 



