6 
that before the establishment of an American standard the tetanus 
serums upon the market varied extravagantly in the unit strength 
claimed, and were, for the most part, comparatively weak in true 
antitoxic potency. Since the promulgation of this standard unit the 
serums on the market have decidedly greater antitoxic value. The 
feebleness of the foreign serums compared with those of American 
manufacture is also evident from the table. 
The object of this bulletin is to describe in detail the methods used 
in preparing and using this standard. A discussion of the theoretical 
considerations is introduced for a better understanding of the prin- 
ciples involved. 
AMERICAN UNIT, AND METHODS OF STANDARDIZATION. 
Definitions. — “The immunity unit for measuring the strength of 
tetanus antitoxin shall be ten times the least quantity of antitetanic 
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.’’ 
The unit was thus officially defined October 25, 1907, in Treasure" 
Department Circular No. 61. This circular amended the regulations 
promulgated in accordance with the act 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 
traffic in said articles, and for other purposes.” 
Based largely upon the work on the standardization of tetanus 
antitoxin done in the Hygienic Laboratory, a special committee of 
the Society of American Bacteriologists, which met in New York 
December 27 and 28, 1906, made the following report, which was 
unanimously adopted : 
Tliat tetanus antitoxin lie standardized hy the tetanus toxin furnished by the 
Public Health and Marine-Hospital Service. The unit is ten times the least amount 
of serum necessary to save the life of a 350-gram guinea pig for ninety-six hours against 
the official test dose of the standard toxin. The test dose is 100 minimal lethal doses 
of a precipitated toxin preserved under special conditions at the Hygienic Laboratory 
of the Public Health and Marine-Hospital Service. It was decided that the minimal 
immunizing dose for a case of possil)le infection through a wound should be 1,500 of 
such units. It was decided that after April 1 the new unit should be adopted by all 
producers of tetanus antitoxin. 
J. J. Kinyoun, Chairm.an. 
Theobald Smith. 
I Herbert D. Pease. 
E. M. Houghton. 
Joseph McFarland. 
M. J. Rosenau. 
William H. Park, Secretary. 
