ISOLATION OF B. TETANI. 



379 



a very characteristic appearance. The spores are round, and in 

 diameter may be three or four times the thickness of the bacilli. 

 They are developed at one end of a bacillus, which thus assumes 

 what is usually described as the drumstick form (Figs. 126, 

 129). Upon rare occasions a spore may form at each pole of 

 a bacillus, producing a dumb-bell form (see Fig. 130). In a speci- 

 men stained with a watery solution of gentian-violet or methy- 



FlG. 129. Tetanus bacilli; some of 

 which possess spores. From a culture in 

 glucose agar, incubated for three days at 

 37 C. Stained with carbol-fuchsin. x 1000. 



FIG. 130. Bipolar spore formation in 

 a glucose agar culture of B. tetani. (Dr. 

 Chas. H. Potter.) x 1000. 



lene-blue, the spores are uncoloured except at the periphery, so 

 that the appearance of a small ring is produced ; if a powerful 

 stain such as carbol-fuchsin be applied for some time, the spores 

 become deeply coloured like the bacilli. Further, especially if 

 the culture preparation be heated, the spores may become free 

 in the culture medium. 



Isolation. The isolation of the tetanus bacillus is somewhat 

 difficult. By inoculation experiments in animals, its natural 

 habitat has been proved to be garden soil, and especially the 

 contents of dung heaps, where it probably leads a saprophytic 

 existence, though its function as a saprophyte is unknown. From 

 such sources and from the pus of wounds in tetanus, occurring 

 naturally or experimentally produced, it has been isolated by 

 means of the methods appropriate for anaerobic bacteria. The 

 best methods for dealing with such pus are as follows : - 



(i) The principle is to take advantage of the resistance of 

 the spores of the bacillus to heat. A sloped tube of inspissated 



