THE PATHOGENIC PROTOZOA 181 



1910, i. U20) says the question of distinguishing the T. 

 pallidum from the S. refringens need not arise, since the 

 latter is rare in the secretion of a chancre, and does not 

 occur in other venereal diseases until a stage so late that 

 a wrong clinical diagnosis is impossible. S. refringens 

 is thicker, has fewer and wider turns to its corkscrew, 

 and is more refractile; while on the other hand, the 

 T. pallidum is finer, has more turns, tapers at both ends, 

 and appears dead white. 



The secretion of a primary sore examined by means of 

 the ' dark ground illumination ' is said to hardly ever 

 fail to reveal the T. pallidum. A chancre is cleansed 

 by washing with normal saline and a drop of clear exudate 

 squeezed out. This is taken up in a capillary tube, placed 

 on a microscope slide and covered with a cover-glass. 

 A drop of cedarwood oil is placed on the under surface 

 of the slide, and contact made with this and the upper 

 surface of the parabolic dark ground condenser. The 

 preparation is examined with a / ; -inch objective. 



The ' dark ground illumination ' allows no rays of light 

 to reach the eye of the observer, except those reflected by 

 certain objects, such as the treponeme, under observation. 

 The treponeme is seen twisting its corkscrew-like form, 

 which is brightly illuminated, across the dark, non-trans- 

 parent background. Neither form nor size is distorted. 

 T. pallidum appears moderately stiff and rigid. Move- 

 ments of flexion and oscillation are not so marked as in 

 some allied species. With the exception of S. dentium, 

 T. pallidum, almost alone among the spirochsotes, retains 

 its spiral arrangement not only during movement but 

 also when at rest. In other words, its spirals represent 

 a permanent arrangement. Dark background illumina- 

 tion can be carried out almost as well on dried as on living 

 preparations. 



Material for microscopic preparations may be obtained 

 by the method recommended by Phillips and Glynn. 

 The lesion is cleansed with cotton-wool, rubbing it with 

 wool, and then swabbing with wool soaked in methylated 

 spirit. At the end of four minutes the spirit is wiped off, 

 and the clear serum which exudes collected in a capillary 

 tube. 



The organism may be stained by Giemsa's stain : 

 Azur II. eosin, 3 grammes; Azur III., 0-8 gramme; 



