PATHOGENIC EFFECTS 421 



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 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 a purulent or foetid dis- 

 charge, though this may be absent. In tetanus following 



* 





Kic. 125. Colonies of the tetanus bacillus on anaerobic 

 agar plates, seven days old. x 50. 



clean operation wounds, catgut ligatures may be the source of 

 infection. Microscopic examination of sections 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 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. It is 

 important to note that the wound through which infection has 



