ANTITETANIC SERUM. 391 



or toxine and the injection of the serum. The longer the 

 interval which is allowed to elapse, not only the greater 

 must be the dose of the serum but the less likely is cure to 

 occur. In animals, where symptoms have fully manifested 

 themselves only a small proportion of cases can be saved. 

 As in other cases, there is no evidence that the antitetanic 

 serum has any detrimental effect on the bacilli. It only 

 neutralises the effects of the toxine. The standardisation of 

 the antitetanic serum is of the highest importance. Behring 

 recommends that for protecting animals a serum should be 

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

 grammes weight of mice against the minimum fatal dose of 

 the bacillus or toxine. A mouse weighing twenty grammes 

 would thus require .00002 gramme of such a serum to 

 protect it against the minimum lethal dose. In the injection 

 of such a serum subsequent 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 obtain- 

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

 For this purpose, as for his later laboratory experiments, 

 he obtained serum by the immunisation of such large 

 animals as the horse, the sheep, and the goat. The prin- 

 ciples of the process were the same as in his earlier work, 

 namely, the injection of toxine, accompanied at first with 

 the injection of iodine terchloride. It was found that 

 the greater the degree of the natural susceptibility of an 

 animal to tetanus, the easier was it to obtain a serum of a 

 high antitetanic potency. The horse was, therefore, the 

 most suitable animal. If now we take for granted that the 

 relative susceptibility of man and the mouse towards tetanus 

 are nearly equal, a man weighing TOO kilogrm. would 

 require . i grm. of the serum mentioned above, to protect 

 him from inoculation with the minimum lethal dose of 

 bacilli or toxine. If symptoms had begun to appear, 100 

 c.c. at once would be necessary, and as the injection of 

 such a quantity might be inconvenient, Behring recom- 

 mended that for man a more powerful serum should be 



