STRUCTURE, MOTIONS, REPRODUCTION. 119 



filaments is homogeneous, but after a time it becomes segmented, 

 and later the protoplasm of each segment becomes condensed into 

 a spherical or oval refractive body, which is the spore. For a time 

 these are retained in a linear position by the cell membrane of the 

 filament (Fig. 75, a), but this is after a while dissolved or broken 

 up and the spores are set free. In liquid cultures they sink to the 

 bottom as a pulverulent precipitate, and upon the surface of a solid 

 medium they form a layer which is usually of a white or yellowish- 

 white color, and which, when examined under the microscope, in old 

 cultures is found to consist almost entirely of shining spherical or 

 oval bodies which do not stain, by the ordinary methods, with the 

 aniline colors. While many of the bacilli during the stage of spore 

 formation grow out into long filaments, others do not, and one or 

 more spores make their appearance in rods of the ordinary length 

 which characterizes the species. These may be located in the centre 

 of the rod or at one extremity (Fig. 75, 6). It sometimes occurs 



c- 



Fia. 75. 



that when a single central spore is formed the rod becomes very 

 much enlarged in its central portion, assuming a spindle shape (Fig. 

 75, c); or one extremity may be enlarged, producing forms such as 

 are shown in Fig. 75, d. Some of the smaller spherical spores mea- 

 sure less than 0.5 yu in diameter, but they are, for the most part, 

 oval bodies having a short diameter of 0. 5 to 1 /< and a long diame- 

 ter of one to two /<, or even more. They are enveloped in a cellular 

 envelope which, according to some observers, consists of two layers 

 an exosporium and an endosporium. 



The germination of spores has been studied by Prazmowski, 

 Brefeld, and others. The process is as follows : By the absorption 

 of water they become swollen and pale, losing their shining, refrac- 

 tive appearance. Later a little protuberance is seen upon one side 

 or at one extremity of the spore, and this rapidly grows out to form 

 a rod which consists of soft-growing protoplasm enveloped in a 

 membrane which is formed of the endosporium or inner layer of the 

 cellular envelope of the spore. The outer envelope, or exosporium, 

 is cast off and may be seen in the vicinity of the newly formed rod 

 (Fig. 76). Sometimes the vegetative cell emerges from one extrem- 



