MICROSCOPIC EXAMINATION OF TISSUES AND EXUDATES 75 



elements stain red, nuclei and leucocytes appear bluish green. Sec- 

 tions stained by Giemsa's method show the fungus elements very 

 clearly in some cases. Hematoxylin and eosin will also usually show 

 them, but their coloring is weak. 



In general, fungus parasites are not so numerous in exudates as 

 bacteria are. One must therefore not be satisfied with a hasty exam- 

 ination but must patiently go over many microscopic fields. Young 

 growing elements of the fungi are all Gram-positive, but old my- 

 celium becomes filled with fat and other materials, and the Gram- 

 staining protoplasm may be but a small portion of the whole. In 

 general, stained smears are not of much use in detecting pathogenic 

 fungi. Some exceptions are: sporotrichosis, where the phagocyted 

 fusiform bodies characteristic of this disease may be best demon- 

 strated in smears of pus; infections with Candida albicans and 

 Cryptococcus neojormans, where the yeast-like bodies may be read- 

 ily demonstrated in smears of pus, sputum, or spinal fluid, stained by 

 methylene blue or by Gram's method; and histoplasmosis, where the 

 small Leishmania-like bodies phagocyted by large macrophages are 

 best demonstrated in smears of bone marrow or splenic pulp, treated 

 like a blood smear, carefully fixed, and stained with Wright's stain 

 or Giemsa's stain. 



In other fungus diseases the procedure of choice is to examine the 

 pus or sputum or other material wet and usually unstained. If not 

 too thick it can be covered with a cover slip and examined without 

 any preparation. Many specimens need to be diluted or digested in 

 one or another type of mounting fluid. The material most frequently 

 used is a solution of sodium or potassium hydroxide. Such a solution 

 serves to dissolve the leucocytes and other tissue elements, or at least 

 to soften them and make them more translucent, without destroying 

 the fungus elements which for the most part are rather resistant to 

 strong alkali. The strength of the solution varies, according to dif- 

 ferent authorities, from 5 to 40 per cent. The stronger the solution 

 is, the quicker its action and the greater the danger of producing 

 artifacts and of destroying the fungus. In general a 10 per cent 

 solution seems to be most useful. A loop of pus or sputum is stirred 

 up in a drop of this solution on a slide, covered with a cover slip, 

 and allowed to stand 15 to 30 minutes before examination. To pre- 

 vent evaporation the edges of the cover slip may be sealed with 

 petroleum jelly. 



A number of other mounting fluids may be used. The Amann's 

 fluid with cotton blue described on page 68 will serve to dilute the 



