DIFFERENTIAL COUNTS 207 



been added i drop of Giemsa's stain for each c.c. just before making 

 the blood examination. 



The best results are obtained when the mixing in the pipette bulb is done im- 

 mediately after taking up the blood and diluent. Recently I have found it necessary 

 to add enough N/i NaOH to the commercial formalin to bring it to about +0.75. 

 To do this add to it a few drops of phenolphthalein as an indicator and continue 

 to add a dilute sodium hydrate or sodium carbonate solution until a pink color 

 just developes at room temperature. This corresponds to about +0.75 with boiling 

 titration. The acidity of commercial "Formalins" varies greatly. Of this +0.75 

 formalin I use i^% in a %% glycerine solution instead of water. 



The usual technic in making the haemocytometer preparation is employed using 

 a Tiirck ruling. Count the leukocytes in the three upper or lower i sq. mm. squares, 

 divide by 3 to obtain an average per sq. mm., multiply by 10 for the content of a 

 cubic millimeter and then by 20 for the dilution. (Blood to 0.5; diluent to n.) 

 This can be done mentally and requires no calculation on paper. Having counted 

 the leukocytes, again go over the same portion of the ruled surface and count the 

 polymorphonuclears and estimate the percentage of these to the total leukocytes. 

 The majority of disrupted cells in a dry-stained preparation are transitionals hence 

 the percentage of polymorphonuclears by this method is lower. 



It is unnecessary in such a count to have an assistant; of course, in making a 

 complete differential count it is preferable to have some one tabulate or laboriously 

 to do this one's self. 



The red cells are practically diaphanous and not disintegrated as 

 when acetic acid is used as a diluent, consequently it is easy to make 

 out the particular red cell as to size, etc., containing a malarial parasite. 



The best results are obtained with a %-inch objective. Higher powers are of 

 course impracticable by reason of the thickness of the cover-glass of the haemocyto- 

 meter. 



The following are the appearances of the various leukocytes. 



Eosinophiles. In these the bilobed nucleus stains rather faintly and the color 

 is greenish blue. The eosinophile granules show easily as coarse, brickdust-red 

 colored particles. 



Polymorphonuclears. The nucleus stains a deep, rich, pure violet but less in- 

 tense than that of the small lymphocyte. The shape of the nucleus is typically 

 three or four lobed but even when of the horseshoe shape of a transitional nucleus 

 is easily recognizable by the intensity of the violet staining. That which makes the 

 polymorphonuclears very easy of differentiation is the distinctness of the cell out- 

 lines produced by the fine yellowish granulations in the cytoplasm. 



Small Lymphocytes. The nucleus is perfectly round and stains a deep violet. 

 It is almost impossible to make out any cytoplasmic fringe. 



Large Lymphocytes. The nucleus here is round and of a lighter violet than that 

 of the small lymphocyte. The cytoplasm is blue, nongranular, and sharply defined 

 from the nucleus. 



Large Mononuclears. These show a washed-out, slate-colored nucleus which 

 blends with the gray slate-blue staining of the cytoplasm so that there is an in- 

 defmiteness of outline in the more or less irregularly contoured nucleus. 



