TETANUS 235 
when subjected to a temperature of 100° C. in water or steam for ten 
minutes. The bacilli in the vegetative state are readily destroyed 
by 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. 
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 is stated by Hutyra and Marek that in these cases it is the other 
bacteria introduced that disturb the tissues thereby enabling the 
spores of the tetanus bacillus to multiply. Infection may follow 
slight abrasions of the skin where infected earth comes in contact 
with the lacerated epidermis. Infection through wounds in the 
intestinal mucosa does not seem to have been clearly demonstrated. 
The most usual method seems to be by pricks and punctures, where 
the virus may be carried well into the tissues 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 neona- 
torum). 
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 thar 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, however, a few exceptionally long periods 
reported. It has been noted by Richter and others that the shorter 
the period of incubation the more severe the disease, the mortality 
being over 90 per cent. in the first and about 50 per cent. when the 
symptoms are slow in appearing. 
Symptoms. The first symptoms are often obscure and may be 
overlooked or they may be ushered in suddenly with violent and exten- 
