THE TO X INKS OF THE BACILLUS. 389 



arising naturally. In artificial injection of toxine part finds 

 its way into the blood stream, and if infected animals be 

 killed during the incubation period there is often evidence 

 of toxine in the blood and solid organs. Rarely, however, 

 during this period, and probably never after symptoms have 

 begun, is there free toxine in the central nervous system. 

 A possible explanation of this will be discussed in the 

 chapter on Immunity. If tetanus toxine be introduced 

 into the stomach or intestine, it is not absorbed. It to 

 a large extent passes through the intestine unchanged. 

 Evidence that any destruction takes place is wanting. 



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, 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. 



