IMMUNITY AGAINST TETANUS 443 



falls into line with the work on the development of supersensi- 

 tiveness to proteids generally (see " Anaphylaxis " under Im- 

 munity). More successful in producing immunity are the 

 methods of accompanying the early injections of crude toxin 

 with the subcutaneous introduction of small doses of iodine 

 terchloride, or of using toxin which has been acted on with iodine 

 terchloride or with iodine itself. Living cultures attenuated in 

 various ways, e.g., by heat, have also been used. By any of these 

 methods susceptible animals can be made to acquire great 

 immunity against large doses of tetanus toxin, and also against 

 living bacilli. Immunity thus acquired remains in existence for 

 a very long time. Not only so, but the serum of such immune 

 animals possesses the capacity of protecting animals susceptible 

 to the disease against a subsequent infection with a fatal dose 

 of tetanus bacilli or toxin. Further, if injected subsequently to 

 such infection, the serum can in certain cases prevent a fatal 

 result, even when symptoms have begun to appear. The degree 

 of success attained depends, however, on the shortness of the 

 time which has elapsed between the infection with the bacilli or 

 toxin and the injection of the serum. In animals where symptoms 

 have fully manifested themselves only a small proportion of cases 

 can be saved. As with other antitoxins, there is no evidence 

 that the antitetanic serum has any detrimental effect on the 

 bacilli. It only neutralises the effects of the toxin. The 

 standardisation of the antitetanic serum is of the highest import- 

 ance. Behring recommends that for protecting animals a serum 

 should be obtained of which one gramme will protect 1,000,000 

 grms. weight of mice against the minimum fatal dose of the 

 bacillus or toxin. A mouse weighing twenty grms. would 

 thus require '00002 grm. of the serum to protect it against the 

 minimum lethal dose. In the injection of such a serum subse- 

 quent to infection, if symptoms have begun to appear, 1000 

 times this dose would be necessary; a few hours later 10,000 

 times, and so on. 



As the result of his experiments, Behring aimed at obtaining 

 a curative effect in the natural disease occurring in man. For 

 this purpose he immunised large animals such as the horse, the 

 sheep, and the goat. It is found that the greater the degree of 

 the natural susceptibility of an animal to tetanus, the easier is it 

 to obtain a serum of a high antitetanic potency. The horse is, 

 therefore, the most suitable animal. If now we take for granted 

 that the relative susceptibilities of man and the mouse towards 

 tetanus are nearly equal, a man weighing 100 kilogrm. would 

 require *1 grm. of the serum mentioned above to protect him 



