PA THOGENIC EFFECTS. 383 



being a strict an&robe. Speculation may commence at the 

 end of twenty-four hours in cultures grown at 37 C. 

 much later at lower temperatures. Like other spores, those 

 of tetanus are extremely resistant. They can usually with- 

 stand boiling for five minutes, and can be kept in a dry 

 condition for many months without being killed or losing 

 their virulence. They have also high powers of resistance 

 to antiseptics. 



Pathogenic Effects. The proof that the B. tetani is the 

 cause of tetanus is complete. It can be isolated in pure 

 culture, and when reinjected in pure culture it reproduces 

 the disease. It may be impossible to isolate it from some 

 cases of the disease, but the cause of this very probably is 

 the small numbers in which it sometimes occurs. 



(a) The Disease as arising Naturally. The disease 

 occurs naturally, chiefly in horses and in man. Other 

 animals may, however, be affected. There is usually some 

 wound, often of a ragged character, which has either been 

 made by an object soiled with earth or dung, or which has 

 become contaminated with these substances. There is 

 often purulent or foetid discharge, though this may be 

 absent. Microscopic examination of sections may show at 

 the edges of the wound necrosed tissue in which the tetanus 

 bacilli may be very numerous. If a scraping from the 

 wound be examined microscopically, bacilli resembling the 

 tetanus bacillus may be recognised. If these have spored, 

 there can be practically no doubt as to their identity, as 

 the drumstick appearance which the terminal spore gives to 

 the bacillus is not common among other bacilli. Care 

 must be taken, however, to distinguish it from other thicker 

 bacilli with oval spores placed at a short distance from their 

 extremities, such forms being common in earth, etc., and 

 also met with in contaminated wounds (Fig. 95). It is 

 important to note that the wound through which infection 

 has taken place may be very small, in fact, may consist of a 

 mere abrasion. In some cases, especially in the tropics, it 

 may be merely the bite of an insect. The absence of a 

 definite channel of infection has given rise to the term 



