Tetanus antitoxin is undoubtedly of great value as a prophylactic and immunizing agent, its efficacy having been fully confirmed by both laboratory studies and numerous clinical experiences. It is highly important, therefore, that a standard unit for this serum should be provided such as now renders the administration of diphtheria antitoxin so accurate and satisfactory. The necessity for such a standard is evidenced by the fact that in this country, until recently, there were as many methods of standardizing tetanus antitoxin serum as there were manufacturers.
The standardization of this serum is a very difficult problem, and a vast amount of study has been devoted to its solution. Work on this subject has been carried on in the Hygienic Laboratory of the Public Health and Marine-Hospital Service for the past two years, with the result that a stable tetanus toxin has been obtained. This toxin, when preserved under conditions of