238 PATHOGENIC BACTERIA. 



an atmosphere of hydrogen upon gelatin plates, somewhat 

 resemble those of the well-known hay bacillus. There 

 is a dense rather opaque central mass from which a more 

 transparent zone is readily separable. The margins of 

 this outer zone are made up of a radiating fringe of pro- 

 jecting bacilli (Fig. 69). The liquefaction that occurs is 

 much slower than that caused by bacillus subtilis. 



When grown in gelatin puncture-cultures the develop- 

 ment occurs deep in the puncture, and consists of mul- 

 titudes of short-pointed processes radiating from the 

 puncture, somewhat resembling a fir tree (Fig. 67). 

 Liquefaction begins in the second week and causes the 

 disappearance of the radiating processes. The liquefac- 

 tion spreads slowly, but may involve the entire mass of 

 gelatin and resolve it into a grayish-white syrupy liquid, 

 at the bottom of which the bacilli accumulate. The 

 growth in gelatin containing glucose is much more rapid ; 

 that in agar-agar punctures is much slower, but similar 

 to the gelatin cultures except for the absence of liquefac- 

 tion. The organism can also be grown in bouillon, and 

 attains its maximum development at a temperature of 

 37 C. Much gas is given off from the cultures. 



Cultures of the tetanus bacillus in all media give off 

 a peculiar characteristic odor a burnt-onion smell, with 

 a suggestion of putrefaction about it. 



The methods for excluding the oxygen from the cul- 

 tures and replacing it by hydrogen, as well as other 

 methods suggested for the cultivation of the strictly 

 anaerobic organisms, are given under the appropriate 

 heading (Anaerobic Cultures), and need not be repeated 

 here. 



Tetanus bacilli exist in nature as widely distributed 

 saprophytes. They are quite common in the soil, and 

 the fact that they are most plentiful in manured ground 

 has suggested that they originate in the intestines of 

 horses and reach the earth from their excrement. I/e 

 Dentu has, however, shown that the tetanus bacillus is 

 a common organism in New Hebrides, where there are no 



