SUSCEPTIBILITY AND IMMUNITY. 271 



young mice through their mother's milk. In his tetanus experi- 

 ments Ehrlich used blood serum from an immune horse to give im- 

 munity to the mother mouse when her young were already seven- 

 teen days old. Of this blood serum two cubic centimetres were 

 injected at a time on two successive days. The day after the first 

 injection one of the sucklings received a tetanus inoculation by 

 means of a splinter of wood to which spores were attached. The 

 animal remained in good health, while a much larger control mouse 

 inoculated in the same way died of tetanus at the end of twenty-six 

 hours. Other sucklings, inoculated at the end of forty-eight and of 

 seventy-two hours after the mother had received the injection of 

 blood serum, likewise remained in good health, while other control 

 mice died. 



The possibility of conferring immunity by means of the milk of 

 an immune animal is further shown by the experiments of Brieger 

 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 vacuo 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 



