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. 
