VITALITY OF SPORES. 229 



oxygen. That is one reason why it is so difficult to cultivate 

 this germ, although it will grow on all kinds of culture-media. 

 It can be habituated to oxygen, but that is done at the ex- 

 pense of its virulence. 



It grows best at the temperature of the body. It is readily 

 stained with the anilin dyes, and also by Gram's method. 

 The spores are stained in the usual manner. When the 

 tetanus bacillus is grown at very high temperatures it pre- 

 sents distinct involution-forms. It is rapidly destroyed by 

 temperatures above 55 C. 



The bacillus of tetanus is grown best in an atmosphere of 

 hydrogen. 



On gelatin plates small white colonies develop in about 

 five days, which are quite characteristic. They have the 

 appearance of a thistle, very fine lines radiating from a dense 

 central mass. The gelatin is gradually liquefied. On agar 

 plates the colonies develop more slowly ; the medium is not 

 liquefied. 



In gelatin stab cultures development occurs along the line 

 of inoculation, without any surface growth, in the form of 

 fine radiating threads which extend from the central line of 

 growth out into the gelatin, an appearance which suggests a 

 fir tree (Figs. 94 and 95). This characteristic appearance is 

 lost when liquefaction occurs at about the end of the second 

 week. A grayish-white viscid liquid fills the centre of the 

 medium, and the culture accumulates at the bottom of the 

 liquefied mass. Agar cultures are not liquefied. 



Plain bouillon or glucose-bouillon is first rendered turbid, 

 but becomes quite clear when the culture settles. The super- 

 natant fluid contains the tetanus toxin. The growth in 

 bouillon is accompanied by the evolution of much gas. A 

 very disagreeable, peculiar odor is given off by all tetanus 

 cultures. 



On potato a moist invisible growth develops. Milk is not 

 changed in appearance. 



Vitality of spores : The spores are quite resistant, and will 

 remain alive for a long time. When exposed to live steam at 

 a temperature of 100 C., they are killed in from five to eight 

 minutes. A much longer exposure is required for tempera- 



