144 THE MORE CHRONIC INFECTIOUS DISEASES 



results positively some form of syphilis is present, although 

 it may not be in a form transmissible to others. Otherwise 

 syphilis is diagnosticated by finding spirochetes in the serum 

 which exudes from chancres, skin eruptions, and mucous 

 patches, or the venereal warts on mucous membranes. This 

 serum is taken and looked at unstained upon a background 

 of India ink or by what is called dark-field illumination, a 

 process by which the light is made to shine upon the body 

 of the spiral from the side. It can also be stained by appro- 

 priate methods, but its minute size and paleness make this a 

 trying test. 



FIG. 43. Treponema pallidum appearing as bright refractive body on a 

 dark field, as shown by India ink or ultramicroscope. (Park.) 



Morphology and General Characteristics. The Spirocheta 

 pallida is a corkscrew-like, actively motile, delicate thread. Its 

 windings assume the form of a large arc of a small circle, and 

 vary from four to twenty. It is 1 o^ o o to 75000" incn wide 

 and from gWo to Woo inch lon S- It; moves by end flagella, 

 in a screwing and waving motion. It is killed rapidly by 

 drying, a very fortunate thing, as many people are thereby 



