264 SUSCEPTIBILITY AND IMMUNITY. 



and Ehrlich (1892). A female goat was immunized against tetanus 

 by the daily injection of " thymus-tetanus bouillon." The dose was 

 gradually increased from 0.2 cubic centimetre to 10 cubic centimetres. 

 At the end of thirty-seven days a mouse, which received 0.1 cubic 

 centimetre of the milk of this goat in the cavity of the abdomen, 

 proved to be immune against tetanus. Further experiments gave a 

 similar result, even when the milk of the goat was not injected into 

 the peritoneal cavity of the mouse until several hours after inocu- 

 lation with a virulent culture of the tetanus bacillus. 



When the casein was separated the milk retained its full im- 

 munizing activity, and by concentration in vacua a thick milk 

 was obtained which had a very high immunization value 0.2 cubic 

 centimetre of this milk protected a mouse against forty-eight times 

 the lethal dose of a tetanus culture. 



In a subsequent communication (1893) Brieger and Ehrlich de- 

 scribe their method of obtaining the antitoxin of tetanus from milk 

 in a more concentrated form. They found by experiment that it was 

 precipitated by ammonium sulphate and magnesium sulphate. From 

 twenty-seven to thirty per cent of ammonium sulphate added to milk 

 caused a precipitation of the greater part of the antitoxin. This pre- 

 cipitate was dissolved in water, dialyzed in running water, then 

 filtered and evaporated in shallow dishes at 35 C. in a vacuum. 

 One litre of milk from an immune goat gave about one gramme of a 

 transparent, yellowish-white precipitate, which contained fourteen 

 per cent of ammonium sulphate. This precipitate had from four 

 hundred to six hundred times the potency of the milk from which 

 it was obtained in neutralizing the tetanus toxin. 



In a still later communication (1893) Brieger and Cohn give an 

 improved method of separating the antitoxin from the precipitate 

 thrown down with ammonium sulphate. The finely pulverized pre- 

 cipitate is shaken up with pure chloroform, and when this is allowed 

 to stand the antitoxin rises to the surface while the ammonium salt 

 sinks to the bottom. By filling the vessel to the margin with chloro- 

 form, the antitoxin floating on the surface can be skimmed off, after 

 which it quickly dries. By this method the considerable loss which 

 occurred in the dialyzer, used in the previously described method, is 

 avoided. 



A most interesting question presents itself in connection with the 

 discovery of the antitoxins. Does the animal which is immune 

 from the toxic action of any particular toxalbumin also have an im- 

 munity for other toxic proteids of the same class? The experimental 

 evidence on record indicates that it does not. In Ehrlich 's experi- 

 ments with ricin and abrin he ascertained that an animal which had 

 been made immune against one of these subtances was quite as sus- 



