364 TETANUS. 



the susceptibility of man be the same as that of a mouse, 

 the fatal dose for him would be .23 of a milligram or about 

 Y^nrths of a grain. 



There is one question which must arise in connection with 

 tetanus, namely : Granted that the B. tetani is so widely 

 present in the soil, how is it that the disease is not more 

 common than it is, for wounds must constantly be contami- 

 nated with such soil ? Experiments by Vaillard throw light 

 on this point. We have seen that unless suitable precau- 

 tions are adopted, in experimental tetanus in animals death 

 results not from inoculation but from an intoxication with 

 toxine previously existent in the fluid in which the bacilli 

 have been growing. According to Vaillard, if spores rendered 

 toxine -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 point 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 simultane- 

 ous injection of other bacteria such as the staphylococcus 

 pyogenes 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. Kita- 

 sato now holds that in the natural infection in man, the 

 presence of tetanus spores along with foreign material such 

 as splinters of wood or other bacteria, is necessary. Spores 

 alone or tetanus bacilli without spores die in the tissues, 

 and tetanus does not result. 



Summary. In view of all the facts available we must 

 thus look on tetanus as caused by the B. tetani. The 

 bacillus gains entrance to the body through wounds or 

 abrasions, and, multiplying locally, produces poisons which 

 diffuse into the tissues and have an elective action as stimu- 

 lants of especially the spinal cord, but the chemical com- 

 position of which is not yet fully known. The enormous 



