Staining 



791 



The block is then placed in diluted water until it sinks to 

 the bottom of the container, and then transferred to a 

 1.5 to 3 per cent, aqueous solution of nitrate of silver in a blue 

 or amber bottle and kept in a dark incubating oven at 37 C. 

 for from three to five days. Finally, it is washed in water and 

 placed in a solution of pyrogallic acid 2 to 4 grams; formol, 

 5c.c. ; distilled water, 100 c.c., and kept in the dark, at room 

 temperature, from twenty-four to seventy-two hours, then 



Fig. 260. Treponema pallidum impregnated with silver. Film 

 prepared from the skin of a macerated, congenitally syphilitic fetus. 

 X 750 diameters (Flexner). The dense aggregation of organisms may 

 indicate agglutination. 



washed in distilled water, embedded in paraffin, and cut. 

 The treponemata are intensely black, the tissue yellow brown. 

 The sections are finally stained with (a) Giemsa's stain for 

 a few minutes, then washed in water, differentiated with 

 absolute alcohol containing a few drops of oil of cloves, 

 cleared with oil of bergamot or xylol, or (6) concentrated 

 solution of toluidin blue, differentiated in alcohol containing 

 a few drops of Unna's glycerin-ether mixture, cleared in oil 

 of bergamot, then in xylol, and mounted in Canada balsam. 



