BACTERIOLOGICAL INTRODUCTION 17 



of bacilli which correspond to the streptococci are 

 called streptothrix filaments. Not unfrequently 

 long threads are formed in which it is difficult to 

 demonstrate the septa which divide the filaments 

 into cells, and these threads are often spoken of as 

 leptothrix filaments. The streptothrix filament is 

 well seen in Fig. 8, together with the remarkable 

 regularity with which the rows of filaments are 

 arranged. The outgrowth of comparatively short 

 bacilli into thread or leptothrix filaments is seen in 

 photograph 7, which also shows many of the bacillary 

 characters which have been mentioned, such as the 

 constancy in diameter, the enormous variation in 

 length, and the passage from forms which are prac- 

 tically cocci, through a succession of transition forms, 

 to the long leptothrix filaments. Among the shorter 

 forms are many diplobacilli or figure of 8 forms. 

 The resemblance to a loosely-twisted spiral which 

 some of the filaments exhibit is apparent only ; the 

 threads are bent bacilli, and they do not form por- 

 tions of a screw or spiral. 



Spirilla. — To this group belong all organisms 

 which occur as spiral cells or in forms derived from 

 the spiral, and a glance through the illustrations of 

 the various spirilla will show that there is great 

 variety in the size of the various organisms, and 



