128 



the same section, even in the same field; they are 

 seen not infrequently in tissues in a state of chronic in- 

 flammation. 



Any one of several agents may be employed for this 

 purpose of differentiating bacteria from surrounding ob- 

 jects by decolorizing the latter; simple immersion in 

 alcohol or ether for some minutes sometimes accom- 

 plishes this result. The preferable agents are, however, 



1, a solution of acetic acid (two to five per cent.), and, 



2, a solution of the carbonate of potassium (one to three 

 per cent.) in water. Immersion of the stained sections 

 in one of these fluids for five to ten minutes usually suf- 

 fices to decolorize the morphological elements other 

 than bacteria, while the latter still retain a brilliant color. 

 It must be remembered, however, that none of these 

 rules is of universal application : different varieties of 

 bacteria exhibit various reactions toward these agents, 

 and some of the aniline dyes are less readily extracted 

 from the nuclei than others ; the blue and the violet are, 

 in my experience, more tractable in this regard than the 

 brown colors. When it is intended to differentiate in 

 this manner the sections should be at first intensely 

 stained, which may be accomplished by the use of 

 stronger aniline solutions, or (preferably) by permitting 

 them to lie for a longer time in the ordinary (two per 

 cent.) solution. 



The prominence of these colored bodies is further 

 enhanced by illumination with the Abbe condenser, 

 whereby refraction outlines are practically obliterated, 

 the colored objects appearing alone simply by virtue of 

 their color against a white background. 



While the cutting of sections requires time and skill 

 not usually possessed by the general practitioner, the 

 preparation of liquids blood, pus, sputum- for the de- 

 tection of bacteria is extremely simple, and can be 

 accomplished without special knowledge, skill, or appar- 

 atus. This is particularly fortunate, since a valuable 

 means for clinical diagnosis is thereby brought within the 

 reach of every one who possesses a microscope, even an 



