PROTECTIVE INOCULATIONS. 357 
the body of a living animal. The test animal selected is the white 
mouse. When the statement is made that a serum has the value of 
1:1,000,000, he means that by an experimental test, made upon white 
mice, it has been ascertained that these animals are protected from 
fatal infection with the minimal lethal dose of a tetanus culture by the 
use of 0.00002 gramme of the serum for a mouse weighing twenty 
grammes. For the cure of tetanus in the mouse, after the first symp- 
toms of the disease have appeared, a dose at least one thousand times 
as great as the immunizing dose is required, and the more advanced 
the progress of the case the greater the dose must be. A serum of 
the strength above indicated, if used for the treatment of a case of 
tetanus in man, should, according to Behring, be employed in doses 
amounting altogether to at least one hundred cubic centimetres—given 
inside of twenty-four hours in doses of twenty cubic centimetres each. 
For persons sixteen years old he would give doses of ten cubic centi- 
metres, and for children under six, five cubic centimetres at a dose. 
The serum of this strength which he had prepared for testing its 
curative value on man was preserved by the addition of 0.5 per cent 
of carbolic acid. 
Rotter (1892) reports a case successfully treated by Behring’s 
serum. In all two hundred and fifty cubic centimetres was adminis- 
tered subcutaneously. The case was not, however, one of the most 
severe forms of the disease. 
Brieger and Ehrlich (1892) have succeeded in immunizing goats 
by means of gradually increasing doses of a culture of the tetanus 
bacillus in thymus bouillon. The amount given at first was 0.2 cubic 
centimetre, and this was gradually increased to ten cubic centimetres. 
At the end of thirty-seven days the animal was found to be immune 
against virulent cultures, and the important fact was demonstrated 
that the immunizing substance (antitoxin) was present in its milk. 
A mouse which received 0.1 cubic centimetre of the milk of this goat 
in the peritoneal cavity proved to be immune against infection as a 
result of inoculation with a tetanus culture. The immunizing value 
of the milk from this goat was found to be 1,600. That is, a dose of 
0.2 cubic centimetre, which was equal to 1:100 of the body weight of 
the animal, protected a mouse from sixteen times the fatal dose of a 
tetanus culture. After precipitation of the casein the milk still pre- 
served its antitoxic power unimpaired, and by concentrating it 7 vacuo 
a fluid was obtained which proved to have an immunizing value of 
5,000. 
Tn a later communication (1893) Brieger and Cohn give the results 
of additional experiments with the milk of immunized goats. Ani- 
