IMMUNITY AGAINST TETANUS 429 



bacilli have been growing. According to Vaillard, if spores 

 rendered toxin-free, by being kept for a sufficient time at 

 80 C., are injected into an animal, death does not take 

 place. It was found, however, that such spores can be 

 rendered pathogenic by injecting along with them such chemicals 

 as lactic acid, by injuring the seat of inoculation so as to cause 

 effusion of blood, by fracturing an adjacent bone, by introducing 

 a mechanical irritant such as soil or a splinter of wood (as in 

 Kitasato's experiments), or by the simultaneous injection of 

 other bacteria such as the staphylococcus j)t/ogenes aureus. These 

 facts, especially the last, throw great light on the disease as it 

 occurs naturally, for tetanus results especially from wounds 

 which have been accidentally subjected to conditions such as 

 those enumerated. Kitasato now holds that in the natural 

 infection in man, along with tetanus spores, the presence of 

 foreign material or of other bacteria is necessary. Spores alone 

 or tetanus bacilli without spores die in the tissues, and tetanus 

 does not result. 



Immunity against Tetanus. Antitetanic Serum. The arti- 

 ficial immunisation of animals against tetanus has received much 

 attention. The most complete study of the question is found 

 in the work of Hehring and Kitasato in Germany, and of Tizzoni 

 and Cattani in Italy. The former observers found that such an 

 immunity could be conferred by the injection of very small and 

 progressively increasing doses of the tetanus toxin. The degree 

 of immunity attained, however, was not high. Subsequent 

 work has shown that the less rich a crude toxin is in modifica- 

 tions of the true toxin, the less useful it is for immunisation 

 procedures. In fact it is doubtful if small animals can be 

 immunised at all by fresh filtrates. In some cases it has been 

 found that the injection of non-lethal doses instead of commen- 

 cing an immunity actually increases the susceptibility of the 

 animal. This observation has recently acquired fresh interest 

 from its falling into line with the work on the development 

 of supersensitiveness to proteids, which is a very common 

 phenomenon (see " anaphylaxis " under Immunity). More 

 successful in producing immunity are the methods of accompany- 

 ing 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. Tizzoni and Cattani also used the method of 

 administering progressively increasing doses of living cultures 

 attenuated in various ways, e.y. by heat. By any of these methods 

 susceptible animals can be made to acquire great immunity, not 



