232 MICROBIOLOGY 



Passive immunization by means of the serum of actively 

 immune animals was first successfully accomplished by 

 Sclavo. 13 This method has been especially investigated and 

 practically applied by Sobernheim. 14 The serum used is pro- 

 duced by actively immunizing sheep. It is necessary to carry 

 immunization to an extremely high degree in order to obtain 

 any appreciable protective power in the serum. This is ac- 

 complished by preliminary treatment with attenuated vaccines, 

 followed by gradually increasing doses of virulent cultures. 

 Treatment continued at intervals of two weeks, for two to 

 three months, usually produces an effective serum. Horses 

 and cattle may also be used for the process, but they are be- 

 lieved by Sobernheim to give less active sera than sheep. 

 Bleeding is done about three weeks after the last injection. 

 The sera are stable and easily preserved. Horses have also been 

 used to produce, the serum. Injections of 20 to 25 cc. of the 

 serum have been found to protect animals from anthrax and 

 to' confer an immunity lasting at times for two months. Ani- 

 mals already infected are said to be saved by treatment with 

 25 to 100 cc. of the serum. 



BACTERIUM ASTHENIAE DAWSON. 



Place in nature. Bacterium astheniae was discovered by 

 Dawson l in 1898. He considered it the cause of the disease in 

 fowls known as "going light." It was isolated from the con- 

 tents of the duodenum and it is not known that it has a habitat 

 in external nature. 



Morphology. A bacterium with blunt ends, varying in 

 size according to the medium on which it is grown, from 1 p 

 to 1.4 /A long and about 0.5 /x wide. It often occurs in pairs. 



Staining. It does not stain in acid or alkaline methylene 

 blue, carbol fuchsin, or in any alcoholic solutions of the various 



"Sclavo. Centralbl. f. Bakt., Bd. XVIII (1895) p. 744. 



14 Sobernheim. Zeit. f. Hyg., Bd. XXV (1897) p. 301; Bd. XXXI 

 (1899) p. 89. 



1 Dawson. Annual Report B. A. I., U. S. Dept. Agric., 1898, p. 

 329. 



