Immunization. 283 



the virus. Such accidents cannot be excluded at the present 

 time, as the virulence of the blood fluctuates considerably in 

 the affected animals, and there is no satisfactory method bj'" 

 which the virulence of each can be established rapidly; there 

 is likewise no quick method for the standardization of the serum. 



In 1905-1906 168 hogs were treated in the United States by the simul- 

 taneous method (2.5-20 ec. serum, and 0.25-5.0 cc. of virulent blood, each separately, 

 but simultaneously injected). Of these 35 (21%) became slightly affected, while 

 15 (9%) succumbed. On the other hand 54 hogs became affected after the injection 

 of the same quantities of virulent blood, and 50 (92.5%) of these succumbed 

 to the disease. When the hogs which had been treated by the method described 

 were exposed on infected premises, they remained healthy with very few exceptions, 

 while all control animals became severely ill, and most of them died. Some experi- 

 ments on suckling pigs showed that immunization may also probably be used with 

 good results at a very early age (Dorset, McBryde & Niles). Up to November, 1909, 

 about 2,000 hogs were treated with satisfactory results, the losses among the inocu- 

 lated animals in infected herds amounting to 5-15%, in herds free from the, 

 disease 0%, whereas among the animals which were not inoculated the losses 

 amounted to 75-89 and 35% (Melvin). 



3. Other Methods of Immunization. The preparation of a 

 potent serum from horses and cattle has not been successful 

 (Uhlenhuth and Hutyra), and except for the method described 

 above there is at the present time no procedure which has 

 been tried in practice sufficiently. 



Marxer prepared a \'accine by shaking, virulent hog blood at 37°0. for four 

 days in 10% uric acid, or for three days with 25% galactose, this vaccine proving 

 effective in immunizing pigs in laboratory experiments. Inoculated animals did 

 not become infected, and failed to infect healthy pigs. For its practical appli- 

 cation it is recommended to inject the animals at intervals of several months, 

 from 3 to 4 times, with 5 cc. of the vaccine. Uhlenhuth and his associates found 

 on the other hand that pigs treated by this method do not acquire an immunity, 

 and that it is not possible to establish an immunity with virus attenuated or killed 

 by either physical or chemical means. 



King employed for a vaccine the serum of horses which had shortly before 

 been injected intravenously with 85-200 cc. of virulent hog serum. On the assump- 

 tion that the virus is gradually attenuated in the body of the horse, he used the 

 blood of a horse which was drawn six hours after the intravenous injection as a 

 vaccine. He treated several hundred hogs by this method in practice, the results 

 however were varied. While apparently favorable results were obtained in several 

 herds, the disease appeared shortly after inoculation in 11 other herds which had 

 hitherto been free from the disease. 



Immunization Against the Bacillus Suipestifer. Before the establishment of 

 the etiology of hog cholera, the immunization experiments were directed against 

 the bacillus suipestifer, as the supposed causative factor of the disease. The prac- 

 tical results however proved entirely unsatisfactory in spite of the apparent good 

 results in laboratory tests on small animals. At present the tedious experimental 

 investigations are only of generally scientiiie interest, as it appears very improb- 

 able that the treatment of hogs with a serum which, although successful against 

 the secondary infection of the bacillus suipestifer, will ever prove of any advan- 

 tage in its practical application. 



Beeently Stedefeder reports on several experiments in which he succeeded in 

 immunizing pigs against the suipestifer disease, which is said to occur independently 

 (see p. 276). The serum was obtained by a preparatory treatment of rabbits, 

 horses and hogs. 



Veterinary Police. The observations made in recent years 

 have proved repeatedly that hog cholera may be limited to 

 single premises or farms, and the losses be reduced in a great 

 measure by the immediate application of suitable methods of 



