PATHOGENIC EFFECTS. 357 



obtaining the soluble products of the organism. There 

 is in it at first a slight turbidity, and later a thin layer of 

 a powdery deposit on the walls of the vessel. All the 

 cultures give out a peculiar burnt odour of rather un- 

 pleasant character. 



Conditions of Growth, etc. The B. tetani grows best at 

 37 C. The minimum growth temperature is about 14 C, 

 and below 22 C. growth takes place very slowly. Growth 

 takes place only in the absence of oxygen, the organism 

 being a strict ancerobe. Sporulation occurs at the end of 

 twenty- four hours in cultures grown at 37 C. much later 

 at lower temperatures. Like other spores, those of tetanus 

 arc extremely resistant. They can usually resist 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 we shall see reason for 

 believing that 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. Suppuration 

 very usually has occurred. On examination, the wound is 

 usually found to consist of an irregular cavity with ragged 

 walls, and microscopic sections show this cavity to be often 

 surrounded by an area of necrosed tissue in which the 

 tetanus bacilli may be very numerous. From the pus the 

 ordinary pyogenic organisms can be isolated. If such pus 

 be examined microscopically, bacilli resembling the tetanus 

 bacillus may be recognised. If these have spored, there 



