DISEASES CAUSED BY SPOROCH^TES 853 



paring such specimens from primary lesions or from lymph glands, 

 to obtain the material from the deeper tissues, and thus as uncon- 

 taminated as possible by the secondary infecting agents present 

 upon the surface of an ulcer, and also as free from blood as possible. 

 It is best to employ a special device known as a "condenser for dark- 

 field illumination " (Dunkel-Kammer-Beleuchtung). This apparatus is 

 screwed into the place of the Abbe condenser. The preparation is 

 made upon a slide and covered with a cover-slip as usual. A drop 

 of oil is then placed upon the upper surface of the condenser 

 and the slide laid upon it so that an even layer of oil, without air- 

 bubbles, intervenes between the top of the dark chamber and the 

 bottom of the slide. An arc light furnishes the most favorable 

 illumination. In such preparations the highly refractive cell-bodies 

 stand out against the black background, and the motility of the 

 organisms may be observed. 21 



The dark-field condenser is without question the easiest method 

 of finding the Spirochaeta pallida. Its use is easily learned and the 

 apparatus is sufficiently cheap so that it lends itself to the use 

 of the clinic and the office. With very little practice it is possible 

 to detect the spirochaete in suspension if care is taken that not too 

 much blood or other solid particles are mixed with the preparation. 

 Should it be impossible to obtain the material scraped from syphilitic 

 lesions in a sufficiently dilute condition it is best to emulsify it in 

 a drop or two of human ascitic fluid. 



EXAMINATION IN SMEARS. The Spirochaeta pallida can not be 

 stained with the weaker anilin dyes, and even more powerful dyes, 

 such as carbol-fuchsin and gentian-violet, give but a pale and un- 

 satisfactory preparation. The staining method most commonly used 

 is the one originally recommended by Schaudinn and Hoffmann. 

 This depends upon the use of Giemsa's azur-eosin stain employed in 

 various modifications. The most satisfactory method of applying 

 this solution is as follows: 



Make smears upon slides or cover-slips, if possible from the depth of the 

 lesions, 'as free as possible from blood. 



Fix in methyl alcohol for ten to twenty minutes and dry. 



Cover the preparation with a solution freshly prepared as follows: 



Distilled water 10 c.c. 



Potassium carbonate 1 : 1,00 . . 5-10 gtt. 



21 For a critical summary of the various methods of dark-field illumination, the 

 reader is referred to an article by Siedentopf, Zeit. f. wiss. Mikrosc., xxv, 1908. 



