BACTERIACE.E I THE SPOROGENIC ANAEROBES 



28l 



of the wound. Wassermann and Takaki have shown that o.i 

 gram of brain substance suspended in salt solution is able to neu- 

 tralize 10 fatal doses of tetanus toxin, forming a loose combina- 

 tion from which the toxin may be set 

 free by drying. Most mammals are 

 very susceptible, although cats and 

 dogs are only slightly so. Birds are 

 relatively resistant and some reptiles 

 are wholly refractory to the tetanus 

 toxin. 



Von Behring and Kitasato in 1890 

 produced immunity in rabbits, and 

 later in horses, by injecting into them 

 toxin to which iodine trichloride had 

 been added, and subsequently unal- 

 tered toxin. The immunized animal 

 was able to survive an injection many 

 times greater than the amount neces- 

 sary to kill a normal animal. More- 

 over, the cell-free blood serum of the 

 immunized animal was found to neu- 

 tralize the poison in a test-tube and 

 to protect a normal animal against 

 fatal doses of it. The new substance 

 of the blood capable of rendering the 

 toxin harmless was called antitoxin. 

 One antitoxic unit of tetanus anti- 



, . i T -r i after Fraenkel and Pfeiffer.) 



toxin, according to Von Behring, is 



the amount which will neutralize 40 million times the amount 

 of fresh tetanus toxin necessary to kill a mouse weighing 15 

 grams (40 million X the 15 + Ms dose) so completely that 

 only a slight local contraction, indicated by a folding of the 

 skin, results from subcutaneous injection of the mixture into a 

 mouse (the L effect). This amount of toxin (40 million X the 

 15 + Ms dose) is generally measured in practice against a standard 



FIG. 114. Bacillus tetani. 

 Stab culture in glucose gelatin, 

 six days old. (From McFarland 



