466 THE SPIROCHETES 



cate, smooth filaments, hooked at both ends. These elements were at first difficult 

 to account for, being sometimes found end to end with normal heavily stained lepto- 

 spiras as if they were terminal flagella of these. Careful search, however, revealed 

 specimens in which a portion of the filament was still clothed with deeply stained 

 spirally wound protoplasm (Fig. 63). 



The axial filaments of leptospiras are far more delicate than those of treponemas 

 and are not spirally wound. Like finer bacterial flagella, they are invisible under the 

 darkfield microscope. They are apparently firm and elastic. 



Leptospira is provided with a thick, almost transparent periplast, which is recog- 

 nizable by darkfield illumination as a narrow clear zone, or halo, around the organism, 

 and in preparations stained for flagella as a grayish or unstained halo (Figs. 71, 74). 

 The indifference of the organism to saponin and to changes in tonicity may be due 

 to the presence of a dense periplast. More prolonged staining results in intense color- 

 ation of the periplast, so dark that the spirally wound protoplasmic coat is obscured. 

 Under these circumstances there appears at one or both ends of the body a peculiar, 

 fragile-looking filament which readily becomes entangled with similar filaments of 

 other organisms (Figs. 57-62). It may be as long as the body of the organism. It 

 appears to be of periplastic origin and is no doubt the empty periplastic sheath from 

 which the axial filament and cytoplasm have escaped. Detached entangled filaments 

 are also found. Filaments of this type have been observed previously and interpreted 

 as flagella. 



The short spiral terminal elements which are found in degenerated leptospiras, 

 but never in fully developed, healthy specimens, resemble short spirilla. They oc- 

 cur in all the pathogenic species, being usually coarser in L. icterohaemorrhagiae 

 (Figs. 67, 68) and occasionally rather long in L. interrogans (Figs. 64, 65). The origin 

 and nature of these elements is not clear, but in all probability they are involuted 

 forms of the terminal portions of the axial filaments. 



To summarize, leptospiras consist of delicate but firm, elastic, smooth, axial fila- 

 ments with hooked ends; closely wound spiral protoplasmic coats; and dense peri- 

 plasts. When the bowlike axial frame is alternately straightened and relaxed by the 

 rhythmic contractions of the spiral protoplasmic body, the result, in a fluid medium, 

 is rotation. When only one end is hooked, the organism is propelled in the direction 

 of the straightened end, as is seen by direct observation of active organisms by dark- 

 field illumination. The direction of progression is frequently reversed by alternation 

 in the position of the hooked and straight ends of the organism, or both ends may be 

 simultaneously stretched and bent. Rotation never ceases in the living organism so 

 long as it is in a fluid medium, but the extension of the hooked ends becomes less 

 frequent and effective as the vigor of the organisms diminishes. The curving of the 

 ends is usually greatest in L. interrogans and least in L. hcbdomadis. The latter type, 

 while active, keeps both ends nearly straight (Fig. 122), but when relaxed in death 

 shows the characteristic terminal hooks. 



40 cc. of 3% silver nitrate a few drops of ammonia, enough to render the solution slightly opalescent 

 (Fontana's ammoniacal silver nitrate solution; Fontana, A.: Pathologica, 5, 205. 191 2-13). The color 

 of the film gradually changes from yellow to dark brown and then to steel graj- or black, only brief 

 heating being necessary. The films must be covered with a Canada balsam mount before examina- 

 tion to prevent fading by exposure to cedar oil. 



