Immunization. 95 



to a certain degree, wliicli virulence they retain if their culti- 

 vation is continued. Cultures attenuated to two different de- 

 grees produce two vaccines with which chickens may be im- 

 munized against virulent infections. 



This method of immunization is of great scientific im- 

 portance but has not proven successful in practice. Irrespec- 

 tive of the inconvenience of this method, in consideration of 

 the relative small value of fowls, the inoculations in their prac- 

 tical applications sometimes cause considerable losses. Fur- 

 thermore, the desired protection is not afforded which is very 

 probably due to the uncertainty of the applied attenuation. 



Pasteur's vaccine produces local necrosis of the muscles and serous 

 inflammation of the connective tissue when injected under the skin of 

 the breast of chickens. The corresponding part of the breast muscle 

 separates from the living tissue towards the end of the second week, 

 whereupon the sequestrum is reabsorbed in 3 to 4 weeks, or is cast off 

 through a fistula which may have formed. Kitt found by repeating 

 Pasteur's experiments with the two original vaccines that both produced 

 such local affection in chickens and ducks, and in the majority of these 

 birds produced an effective immunization. On the other hand, pigeons, 

 rabbits and small birds were killed by the inoculation. 



Attempts to prepare suitable vaccines from cultures through 

 attenuation at higher temperatures (Salmon, Jess) and through the 

 addition of chemicals (Jess) were unsuccessful. 



Lignieres recommends his polyvalent vaccine (see page 84) against 

 chicken cholera, and in this disease the best results are supposed to 

 have been obtained. The dose consists of % cc. (subcutaneously). 



II. Immunization with immune serum. Kitt (1892) es- 

 tablished by experiments that the blood of chickens immunized 

 against cholera has an immunizing effect upon healthy chickens, 

 and further that the white and yolk of eggs of immune chickens 

 (5 to 10 cc.) possesses a similar effect. Later Kitt & Mayr 

 (1897) prepared a serum by means of intravenous injections 

 of virulent cultures in horses of which 2 to 20 cc. produced pas- 

 sive immunity in rabbits and % to % cc. in mice, nevertheless 

 it was ineffective in chickens. Still later Kitt (1902-3) produced 

 an active immunity in rabbits by injecting them subcutaneously 

 first with immune serum from chickens or horses (1 to 10 cc.) 

 and following this with the injection of virulent cultures. 

 Eabbits highly immunized in this manner produce a serum of 

 which 1^ to 3 cc. protect rabbits and mice against a virulent 

 infection, and in some cases chickens and pigeons were also 

 immunized with it. Finally Kitt obtained a serum from horses 

 by subcutaneous injection of virulent cultures, of which 2 

 to 5 ce. conveyed effective protection to rabbits, geese, ducks, 

 chickens and sometimes also to pigeons against a fatal cutaneous 

 or subcutaneous infection. The immunity develops not later 

 than 24 hours, and is also effective against intestinal infection. 



The serum inoculations naturally produce a passive im- 

 munity lasting only from 1 to 2 weeks, and therefore their 



