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 7m 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 
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- 
