MORPHOLOGY 725 



of serum and virus is without effect on monkeys, but the serum alone is 

 useless when the virus has been already inoculated. No immunizing sub- 

 stances are present in the blood of persons suffering from the disease nor in 

 the broken-down tissues of gummata. 



SECTION II. MORPHOLOGY. 

 1. Microscopical appearance. 



The Treponema pallidum may be examined in the fresh, unstained condition 

 with an ordinary microscope if a powerful source of light (e.g. an inverted 

 incandescent burner) (fig. Ill, p. 118) and a good oil-immersion lens be used. 

 Under these conditions, the organism appears as a small, spiral filament with 

 pointed ends and exhibits very active movements of rotation and flexion. 

 The spiral arrangement is equally evident when the treponema is actively 

 moving and when it is at rest : the spiral is complete and has a corkscrew 

 appearance. 



The examination of treponemata in the fresh condition is much facilitated 



FIG. 344. Treponema pallidum. Scraping from an hard chancre. Dark- 

 ground illumination. Epithelial debris, leucocytes, bacteria and treponemata. 

 (After Gastou.) 



by the use of dark-ground illumination (p. 123) which is also of great 

 assistance when making a diagnosis. With the ultra-microscope the trepo- 

 nema appears as a brilliant spiral standing out sharply against the black 

 background of the field, of the microscope; it exhibits more or less rapid 

 movements of progression, and seems to turn rapidly on itself like a screw 

 and to move like an eel. Sometimes the treponemata have the appearance 

 of " a series of brilliant scintillating points travelling one behind the other 

 in a straight or sinuous line, keeping their respective distances in a sort of 

 Indian file procession " (Gastou). 



When stained, the treponema measures 6-15/x long and about 0'25/x across. 

 Occasionally much longer forms are encountered ; these consist of several 

 parasites attached to each other end to end. The transverse section of the 

 organism is circular. 



The turns of the spiral are perfectly regular especially about the centre of 



