268 TETANUS 



stroyed when subjected to a temperature of ioo° C. in water or 

 steam for ten minutes. The bacilli in the vegetative state are 

 readily destroyed by the usual strong disinfectants, such as 5 

 per cent carbolic acid. 



A number of bacilli closely resembling B. tetani have been 

 described. This renders a careful study of the suspected 

 organism necessary, as it is difficult in some cases to determine 

 B. tetani microscopically. The guinea pig inoculation affords 

 a ready means of differentiation whenever fresh material is 

 available. 



§ 192. Mode of infection. As the bacillus of tetanus 

 is widely distributed in the soil and consequently on articles 

 contaminated with it, the most common modes of infection are 

 punctures, scratches, and pricks made by splinters, nails or 

 infected instruments (traumatic tetanus). It may follow 

 slight abrasions of the skin where infected earth comes in con- 

 tact with the lacerated epidermis. Infection through wounds 

 in the intestinal mucosa do not seem to have been clearly dem- 

 onstrated. The most usual method seems to be by pricks 

 and nail punctures, in which case the virus can be carried well 

 into the living tissue and there is little or no bleeding to wash 

 it out. Infection often occurs in young foals and lambs 

 through the freshly broken umbilical cord (tetanus neon- 

 atorum). 



The period of incubation. The shortest period which 

 seems to be reported is a few hours and the longest is six 

 weeks. In horses the period of incubation is usually from four 

 to twenty days. After inoculation with pure cultures it is 

 from four to five days and in sheep from two to four days. In 

 guinea pigs inoculated with infected soil the incubation period 

 is usually not over forty-eight hours and often less than that. 

 Park has found that mice, guinea pigs, rabbits, rats, 

 horses, goats and a few other animals inoculated with pure 

 culture have a period of incubation of from one to three days. 

 In man it varies from one to twenty days. There are, how- 

 ever, a few exceptionally long periods reported. It has been 



