284 BACILLI OF THE TYPHOID GROUP 



intravenously with defibrinated disease-producing blood in the pro- 

 portion of 5 c.c. of blood for each pound of body weight, and after 

 an interval of a week, if the hog has recovered, repeat the injection. 



3. Intra-abdominal Injections. Inject the immune intra-abdom- 

 inally with defibrinated disease-producing blood in the proportion of 

 10 c.c. of blood for each pound of body weight. 



The danger of spreading the disease by immune-infected hogs 

 disappears within twenty-four hours after an injection, because after 

 this lapse of time, as has been shown by Uhlenhut, their drawn blood 

 cannot transfer the disease; evidently the virus has been neutralized 

 in the body of the immune animal. After an immune hog has recovered 

 from the effects of the last injection of the virulent blood (generally 

 in eight to ten days) its blood can be drawn to inject and immunize 

 unprotected hogs. Blood may be drawn from the hyperimmunized 

 animal by severing the carotid artery and bleeding it to death or by 

 cutting off the tail. The latter method is preferable for the first 

 drawings, as the bleeding may be stopped at any time, thus per- 

 mitting the immune animal to live and to be used again to procure 

 further supplies of blood. Experiments have shown that after hyper- 

 immunization blood may be drawn from the tail three or four times 

 at intervals of a week, without perceptibly lessening the antitoxic 

 properties of the serum obtained. One week after the last collection 

 of blood the serum animal may be killed by severing the carotid and 

 collecting all the blood that can be obtained. The serum of the 

 blood is separated from the clot in the usual manner after coagulation 

 has taken place. A fraction of a per cent, of carbolic acid is added 

 to the serum. Different sera obtained are generally mixed and the 

 efficacy of the mixture is then tested as follows: Eight young pigs 

 weighing from thirty to sixty pounds receive subcutaneously each 2 c.c. 

 of blood from an acute case of hog cholera, two of the pigs treated 

 remain unprotected and the other six are protected in groups of two by 

 the injection, respectively, of 10 c.c., 15 c.c., and 20 c.c. of the immune 

 serum. A good immune serum should protect in a dose of 15 c.c. or 

 less. If this is found to be the case, 20 c.c. of the serum is used as an 

 immunizing dose to protect young pigs weighing from twenty to one 

 hundred pounds. The injection is generally made on the inside of 

 the hind leg. The passive immunity so produced lasts for several 

 weeks only; to produce a more lasting effect, however, the simul- 

 taneous method is used in which 20 c.c. of the immune serum is 

 injected on one side of the animal, while the other receives a small 

 amount (about 2 c.c.) of virulent blood from a case of hog cholera. 



Agglutination of Bacillus Suipestifer by the Serum of Hogs Hyper- 

 immunized against Hog Cholera. The first tests to ascertain whether 

 the serum of hogs sick with hog cholera would agglutinate the hog 

 cholera bacillus in high dilutions were made by Dinwiddie. His 

 results were negative. McClintock, Boxmeyer, and Siffer found that 

 the serum of normal hogs agglutinated the hog cholera bacillus in a 



