PATHOGENIC EFFECTS. 381 



faction of the gelatin takes place, with slight gas formation. In 

 agar the growth is somewhat similar, consisting of small nodules 

 along the needle track, with irregular short offshoots passing 

 out into the medium (Fig. 134, A). There is 

 slight formation of gas, but, of course, no lique- 

 faction. Growth also occurs in blood serum and 

 also in glucose bouillon under anaerobic condi- 

 tions. The latter is the medium usually employed 

 for obtaining the soluble products of the organ- 

 ism. 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 unpleasant character. 



Conditions of Growth, etc. The B. tetani 

 grows best at 37 C. The minimum growth tem- 

 perature 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 anaerobe. Sporulation 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 withstand 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 culture* of' The^te- 

 resistance to antiseptics. tanus bacillus in 



Pathogenic Effects. The proof that the B. sho^Sg thejtS^i 

 tetani is the cause of tetanus is complete. It can shoots (Kitasato). 



.... , , . . , Natural size. 



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 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 dis- 

 charge, though this may be absent. Microscopic examination 



