TETANUS ANTITOXIN 509 



now employed, and the strength of the antitoxic serum is 

 usually described in American units. 1 



The American immunity unit is defined as being ten 

 times the least quantity of anti-tetanic serum necessary 

 to save the life of a 350-grm. guinea-pig for ninety-six 

 hours against the official test dose of a standard toxin 

 furnished by the Hygienic Laboratory. Public Health and 

 Marine Hospital Service, U.S.A. The test dose of the 

 American standard toxin (which is a dry powder) is 

 0-0006 grm., and it contains 100 minimal lethal doses for 

 guinea-pigs of 350 grm. weight. This is, therefore, the 

 L + dose of toxin, analogous to the L + dose of diphtheria 

 toxin used for standardising diphtheria antitoxin (but note 

 that whereas the unit of diphtheria antitoxin corresponds 

 approximately to 100 lethal doses of diphtheria toxin, the 

 unit of tetanus antitoxin corresponds to 1,000 lethal doses 

 of tetanus toxin). 



Tetanus antitoxin for treatment should contain not less 

 than 150 U.S.A. units per c.c. 



The antitoxic treatment of declared tetanus has not 

 proved so successful as that of diphtheria. Two reasons 

 may explain this difference : firstly, tetanus toxin is 

 much more potent than diphtheria toxin, and secondly, 

 tetanus is recognised only when grave injury to the central 

 nervous system has already occurred. In fact, tetanus at 

 an early stage corresponds with diphtheria at a late stage. 

 There can be no question, however, that antitoxin should 

 always be administered in a case of tetanus. In mild 

 cases, 10,000 U.S.A. units may be given intra-muscularly, 

 followed at three-day intervals by two doses of 5,000 units. 

 In severe cases intrathecal administration should be 

 practised 15,000-20,000 units, which may be repeated 



1 On the standardisation and therapeutic use of tetanus antitoxin, see 

 Hewlett's Serum Therapy, 1910 ; MacConkey, Brit. Med. Journ., Oct. 10, 

 1914 ; various authors, Lancet, 1917, vol. i, pp. 673 et seq. 



