TREASURY DEPARTMENT. 
Public Health and Marine-Hospital Service of the United States. 
Walter Wyman, Surgeon-General. 
HYGIENIC LABORATORY.— BULLETIN No. 21. 
1905 . 
THE IMMUNITY UNIT 
FOR STANDARDIZING 
DIPHTHERIA ANTITOXIN 
(BASED ON EHRLICH’S NORMAL SERUM) 
Official Standard prepared under the Act approved July 1, 1902. 
BY 
M. J. ROSENATJ, 
DIRECTOR OF THE HVGIENIC LABORATORY. 
WASHINGTON: 
GOVERNMENT PRINTING OFFICE. 
1905. 
