294 SPECIFIC MICRO-ORGANISMS 



toxin is allowed to stand 30 minutes before injection. Comparable 

 results are obtained only by following a definite procedure and it 



is especially necessary to use the conventional dose of — ~ 



1000 



antitoxic unit and toxic unit in the standardization of sera. 



1000 



The standard unit employed in the United States is some- 

 what different from the Von Behring antitoxic unit. The Ameri- 

 can immunity unit of tetanus antitoxin is ten times the least 

 amount of antitetanic serum necessary to preserve the life of a 



Fig. 118. — Clostridium botidinum. Some individuals containing spores. {After van 



Ermengem.) 



guinea-pig weighing 350 granjs for 9,6 hours against the official 

 test dose of standard tetanus toxin furnished by the Hygienic 

 Laboratory of the U. S. Public Health Service.^ Tetanus anti- 

 toxin deteriorates with moderate rapidity. The reaction be- 

 tween tetanus toxin and antitoxin seems to take place in two 

 stages, first a reversible absorption and following this a specific 

 chemical union. 



' Rosenau and Anderson: U. S. Hygienic Laboratory, Bulletin No. 43, 1908, p. 59. 

 The ofl&cial test dose of toxin is 100 times the amount of a dry tetanus toxin required 

 to kill a 350 gram guinea-pig in four days. 



