IMMUNITY BY FEEDING. 433 



filtered through a Chamberland or other porcelain filter. 

 The filtrate contains the toxines, and it may be used 

 unaltered, or may be reduced in bulk by evaporation, or may 

 be evaporated to dryness. The process of immunisation 

 by the toxine is started by small non-lethal doses of the 

 strong toxine, or by larger doses of toxine the power of which 

 has been weakened by various methods (vide infra). After- 

 wards the doses are gradually increased. Immunity pro- 

 duced in this way is effective not only against the toxine, 

 but also against large doses of the virulent organism in a 

 living condition. This method was carried out with a 

 great degree of success in the case of diphtheria, tetanus, 

 malignant oedema, and other organisms. It appears 

 capable of very general application, though, in the case of 

 some organisms, it is difficult to get a very active toxine 

 from the filtered cultures. It has also been applied in 

 the case of snake poisons by Calmette and Fraser, and a 

 high degree of immunity has been produced. 



Immunity may also be obtained by means of certain 

 chemical substances separated from filtered bacterial cul- 

 tures, though these substances are generally in a more or 

 less impure condition. Hankin was the first to obtain 

 this result by means of an albumose separated from 

 anthrax cultures. 



Though, as already stated, none of these metho can 

 be used directly as curative agents, seeing that they .iply 

 previous treatment before exposure to infection, ye they 

 supply the means of developing a very high deg- e of 

 immunity, which is the first stage in the productioi >f an 

 active curative serum. 



Immunity by Feeding. Ehrlich found that mice could 

 be gradually immunised against ricin and abrin by fe* ding 

 them with increasing quantities of these substances, which 

 are vegetable poisons of enormous potency, and which 

 exhibit an intensely necrotic action at the site of inoculation. 

 In the course of some weeks' treatment in this way the 

 resulting immunity was of so high a degree that the 

 animals could tolerate 400 times the originally fatal dose 

 28 



