THE GENUS SPIROCHETA AND ALLIES 229 



sexual cycle have been too fantastic for belief. Prowazek ('06) 

 observed curious local swellings in Treponema gallinarum and Sf. 

 huccalis, which he regarded as similar to those seen by Heydenreich 

 in Sp. recurrentis, by Perrin in Sp. balbianii, and by Keysselitz in 

 Sp. cmodontw, all of which he interpreted as possibly indicating a 

 sexual process. Swellengrebel's and Fantham's observations on Sp. 

 balbianii leave little reason to doubt that in this form, at least, the 

 structures in question are the results of abnormal or degenerative 

 processes. Krzysztalowicz and Siedlecki ('05) described a complex 

 cycle of Treponema pallidum, involving many form changes, including 

 a so-called trypanosome stage, and sexually differentiated gametes. 

 In their more extended and very valuable paper of 1908 they express 

 doubt as to this earlier interpretation,^ but give most convincing evi- 

 dence of the manifold form changes which these organisms may assume 

 under normal conditions. Muhlens ('07) and many others have noted 

 the same polymorphism, enough, indeed, to show that no one standard 

 of form or size can be depended upon in identifying Tr. pallidum. 

 The most marked and characteristic of these varieties are the short and 

 thick forms with from two to four nodes (noted also by Muhlens and 

 Hartmann in Sp. dentium and buccalis). The other variations shown 

 in Fig. 90 are sufficient to indicate the difficulty in distinguishing this 

 spirochete from other harmless ones and the danger of basing diagnosis 

 upon structures alone. Krzysztalowicz and Siedlecki, who have 

 studied this species for years, admit that they cannot distinguish some 

 stages in its life history from other spirochetes. They conclude that 

 the ring forms (Fig. 90, B) are resting stages, the baguette forms 

 stages during the "period of depression," while the oblong or granu- 

 lar forms are involution or degeneration types. The curious and 

 interesting structures called Cytoryctes luis by Siegel ('05) may well be 

 stages of unknown significance in the life history of Tr. pallidum; 

 they certainly have no resemblance to the bodies described by 

 Guarnieri ('92) under the generic name of cytoryctes (see p. 307), 

 but do recall the "spindle-formed bacilli" found by Seitz and inter- 

 preted by Silberschmidt, Wechselmann, Lowenthal, and others as 

 stages in the life history of Spirocheta vvncenti. 



So-called encysted forms of spirochetes have been mentioned from 

 time to time. Breinl and Kinghorn ('06) suggest that Sp. duttoni, 

 which they found occasionally coiled up within a definite membrane, 

 represent the encysted state of this organism, while "resting stages" 

 have been noted by many different observers in different species of 

 spirochetes without, however, their significance being known. 



F. Mode of Life and Change of Hosts. — Many of the spirochetes 

 are undoubtedly intracellular parasites, although differences of opinion 



1 A vrai dire, nos etudes ulteriures nous ont inspire beaucoup de doutes d cet egard, p. 221. 



