METHOD OF PREPARING AND EXAAIINING THICK-FILMS 359 



good Giemsa stain and a proper diluting water. The length of time 

 for staining as well as for decolorization may vary with the 

 dilution of the stain, the amount of stain per slide and the average 

 thickness of the hlood films. A very little experience with known 

 positives will serve as a guide. The red of the chromatin of the 

 parasites and the blue of the cytoplasm should stand out dis- 

 tinctly against the background. 



Wlien the background is deep blue and the leucocytes almost 

 black the preparation is overstained and the red of the chromatin 

 may be somewhat obscured. Overstaining is apt to occur when 

 only a few slides are left for a full hour in a large amount of 

 stain. When the leucocytes in the thicker parts of the film are pale, 

 the preparation is understained. Sometimes there is enough well- 

 stained area at the margin or in the thinner parts of a preparation 

 to serve, but, especially when a whole batch of slides is under- 

 stained, it is best to restain. 



Two or more blocks can be stained at once in a larger dish. In 

 the staining and decolorizing specimens an interval timer clock 

 will prove to be a useful monitor. 



After staining the block may be placed on a piece of blotting 

 paper to drain and dry at room temperature or in the incubator. 

 It may be then set away in a dry, dark place free from dust and 

 kept for weeks before examination. When the blocks are to be 

 kept for some days it is best to replace the rubber bands with 

 string, unless very strong bands have been used. 



During the whole process of staining, and during storage, the 

 position of the slides in a block is not changed, so that they 

 remain in the same order in which they were taken. 



Thin films may be made on the same slide as the thick, and the 

 slides labelled with an ordinary lead pencil in the thin film. In 

 ordinary surveys it is not necessary to make thin films of all 

 cases. When they are employed they need not be stained unless 

 they are desired for some particular purpose — confirmation of 

 the results obtained in the thick-film, for example. Then they 

 may be stained by the method of Wright, Leishman or any thin- 

 film technique preferred. A thick line made with a wax pencil 

 may be drawn across the slide to keep the stain used in the thin 

 film from spreading over the thick. We have found Pappenheim's 

 Panchrome (obtainable from Karl Hollborn, Leipzig), diluted 

 with water and used as one does Giemsa, an excellent stain for 



