188 INFECTION AND IMMUNITY. 



the precipitate collected on filter paper and the 

 moisture pressed partially out with filter paper. 



The precipitate is then dialized in parchment 

 paper in running water for three days, a small 

 amount of chloroform being added as a pre- 

 servative. 



One-half of one per cent, sodium chlorid is then 

 added and the solution filtered twice through 

 Berkefeld filters. 



In a similar way the U. S. Government has 

 provided for the establishment of a legal tetanus 

 antitoxin unit and the control of serum production. 



Owing to the fact that tetanus toxin is very 

 stable, the toxin itself is kept for comparison 

 instead of the antitoxin as in diphtheria. 



"The immunity unit for measuring the strength 

 of tetanus antitoxin shall be ten times the least 

 quantity of antitetanus serum necessary to save 

 the life of a 350 gram guinea-pig for ninety-six 

 hours against the official test dose of a standard 

 toxin furnished by the Hygienic Laboratory of the 

 Public Health and Marine-Hospital Service. 7 " 



That the United States government is attempt- 

 ing to guard the quality of antitoxins on sale in 

 our markets is apparent from the following state- 

 ment : 8 



"EXAMINATION OF SERUMS MADE BY LICENSED 



MANUFACTURERS. 8 



"The act of Congress, approved July 1, 1902, entitled 

 'An act to regulate the sale of viruses, serums, toxins and 

 analogous products in the District of Columbia, to regulate 

 interstate commerce in said articles, and for other pur- 



7. Bulletin No. 43, Hygienic Laboratory. 



8. From Rosenau, "The Immunity Unit for Standardizing 

 Diphtheria Antitoxin," Bulletin No. 21 of the Hygienic 

 Laboratory of the Public Health and Marine Hospital Service 

 of the United States. 



