BACILLUS TETANI. 535 



plates or Esmarch tubes of slightly alkaline gelatin are 

 made with very small amounts of the culture and kept 

 in an atmosphere of hydrogen (see page 220). They 

 are then kept at from 18 to 20 C., and at the end 

 of about a week the tetanus bacillus begins to appear 

 in the form of colonies. After about ten days the 

 colonies should not only be examined microscopically, 

 but each colony that has developed in the hydrogen 

 atmosphere should be obtained in pure culture and 

 again grown under the same conditions. The colonies 

 that grow only without oxygen, and which are com- 

 posed of the pin-shaped organisms, must be tested upon 

 mice. If they represent growths of the tetanus bacillus, 

 the typical clinical manifestations of the disease will be 

 produced in these animals. 



In obtaining the organism from the soil much diffi- 

 culty is experienced. Here are encountered a number 

 of spore-bearing organisms that are facultative in 

 their relation to oxygen, and are therefore very difficult 

 to eliminate ; and there is, moreover, one in particular 

 that, like the tetanus bacillus, forms a polar spore. 

 This spore is, however, less round and much more oval 

 than that of the tetanus bacillus, and gives to the 

 organism containing it more the shape of a javelin (or 

 clostridium, properly speaking) than that of a pin, the 

 characteristic shape of the spore-bearing tetanus organ- 

 ism. It is non-pathogenic, and grows both with and 

 without oxygen, and should, consequently, not be mis- 

 taken for the latter bacillus. It must also be borne in 

 mind that there are occasionally present in the soil still 

 other bacilli which form polar spores, and which, when 

 in this stage, are almost identical in appearance with 

 the tetanus bacillus ; but they will usually be found to 



