390 TETANUS. 



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. 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 toxin. 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 toxin. 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, looo 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, 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 principles of the process were 

 the same .as in his earlier work, namely, the injection of toxin, 

 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 it was 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 lOO kilogrm. would require .igrm. of 

 the serum mentioned above to protect him from inoculation 

 with the minimun lethal dose of bacilli or toxin. 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 recommended that for man a more powerful serum 

 should be obtained, viz., a serum of which one gramme would 



