SPECIAL METHODS. 435 



blood or clinical microscopy. The malarial plasmodia are best 

 detected in perfectly fresh blood, examined immediately with an 

 immersion-Ion;-:, when their changes of form serve to make them 

 more easily recognizable than when they are sought in smears. In 

 the latter they may be stained by the following method : 



a. Fix the film by means of heat, or, better, by immersion in 

 absolute alcohol for half an hour. (In the latter case wash off the 

 alcohol with water before staining.) 



6. Stain for several hours in Chenzinsky-Pehn's stain : 



Concentrated alcoholic solution of methylene-blue, 10 cc. 

 0.5 per cent, solution of eosin in 70 per cent, alcohol, 5 cc. 

 Distilled water, 10 cc. 



The solution should be filtered before, and preserved from evap- 

 oration during, the staining. 



c. Wash in water, dry, mount in xylol-dammar. 



The malarial plasmodia will be stained blue, the body of the red 

 corpuscles red, the nuclei of the leucocytes blue, and eosinophile 

 granules, within those cells, red. 



6. Examination of Bacteria in Cover-glass Preparations. If the bac- 

 teria are already in a fluid, a drop is placed upon a cover-glass, spread 

 over its surface, allowed to dry spontaneously, and then fixed by heat, 

 as described above. If cultures on solid media are to be examined, 

 a drop of water is first placed upon the cover-glass, and a little 

 mass of the bacteria disseminated through it, and then the mixture 

 is spread in a thin layer by means of the platinum needle. It is 

 then dried and fixed, as in the preceding case. Such preparations 

 may be stained with methylene-blue, carbol-fuchsin, by Gram's 

 method (anilin-gentian-violet, followed by Gram's iodine solution, 

 and then alcohol), or with some other anilin-dye. For the diph- 

 tlierin or typhoid bacillus an alkaline methylene-blue (see Unna's 

 formula) serves well. 



7. Examination in Hanging Drop. This method is useful for the 

 observation of objects suspended in a fluid. It is extensively used 

 in bacteriology fur the study of living bacteria. A drop of the 

 fluid is placed on the centre of a cover-glass, which is then inverted 

 over the concavity in a hollowed slide. 'Flic edges of the cover- 

 glass should then he sealed with a drop of water or oil, to prevent 

 evaporation of the hanging drop. 



