PATHOGENIC EFFECTS 



425 



They have also high powers of resistance 



losing their virulence, 

 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 re-injected 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 natwally. — The disease occurs 

 naturally, chiefly in horses and in man. Other animals may, 

 however, be affected. In different animal species variations in 



Fig. 124. — Colonies of the tetanus bacillus on anaerobic 

 agar plates, seven days old. x 50. 



the clinical progress of the disease are observed. In man and in 

 the horse the spasms early affect the extensor muscles of the 

 trunk, while in other animals they may first appear in the 

 muscles neighbouring on the site of infection. There is in most 

 cases a definite 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 a purulent or foetid discharge, though this may be 

 absent. In tetanus following clean operation wounds, catgut 

 ligatures may be the source of infection. Microscopic examina- 

 tion of septions may show at the edges of the infected wound 

 necrosed tissue in which the tetanus bacilli may be very 

 numerous. If a scraping from the wound be examined micro- 



