430 TETANUS 



only against many times the fatal dose of tetanus toxin, but 

 also against injections of the living bacilli. The degree of 

 immunisation thus acquired remains in existence for a very long 

 time. Not only so, but when a high degree of immunity has 

 been produced by prolonged treatment, it is found that the 

 serum of immune animals possesses the capacity, when injected 

 into animals susceptible to the disease, of protecting them 

 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 

 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 the 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 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, by 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 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 

 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 from inoculation 

 with the minimum 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, 



