434 HISTOLOGICAL TECHNIQUE. 



the nuclei of cells will be blue. This method, like all others used 

 for the detection of the tubercle bacillus, depends upon the fact that 

 that bacillus takes up colors with reluctance, but, after staining, 

 holds them tenaciously. The specimen is therefore first stained 

 with a strong dye, is then decolorized with some agent that will 

 discharge the color from all bacteria except the tubercle bacillus 

 (and spores, which, however, have a different shape from that of 

 the tubercle bacillus), and afterward stained with a weaker dye of 

 another color which is imparted to the bacteria that have been 

 decolorized. 



4. Examination of Urethral Pus for the Gonococcus. The gono- 

 coccus is shaped a little like a coffee-bean, and usually occurs in 

 pairs with the flattened surfaces of the individual cocci facing each 

 other. In pus it is frequently situated within the leucocytes, while 

 the other varieties of pyogenic cocci usually lie outside of the pus- 

 corpuscles. The gonococcus is decolorized by treatment with Gram's 

 iodin solution followed by alcohol; the more common cocci found 

 in suppuration are not decolorized. These differences in shape, sit- 

 uation, and behavior toward dyes serve to distinguish the gonococci 

 from the other cocci that may be present. The smears, fixed by 

 heat, are stained as follows : 



a. Stain for five minutes in freshly filtered anilin-gentian-violet. 

 6. Wash off excess of dye with water. 



c. Immerse in Gram's solution for two minutes. 



d. Decolorize in 95 per cent, alcohol till no more color is given off. 



e. Stain two minutes in aqueous fuchsin, prepared in a manner 

 similar to that used for aqueous methylene-blue. Bismarck-brown 

 may be used for .this counterstain in place of the fuchsin. 



/. Wash in water, dry, and mount in dammar or balsam. The 

 gonococci will be stained by the second dye used ; other cocci be- 

 longing to the pyogenic group will be a dark purple, they having 

 retained the color first imparted to all the bacteria by the gentian- 

 violet. In this case the gonococci are distinguished from the other 

 cocci by taking advantage of the fact that they are " negative to 

 Gram," while the others are " positive." 



5. Examination of Blood-smears. Hsematoxylin, followed by a 

 strong counterstain with eosin, will furnish useful specimens for 

 most purposes. The differentiation of the various granules in the 

 white corpuscles described by Ehrlich requires special methods, for 

 a description of which the reader is referred to special works on the 



