178 'MICROMETRY AND BLOOD PREPARATIONS 



While waiting for the film to stain one has five or six minutes which 

 could not be better spent then in examining the fresh specimen which 

 only requires a moment to make. 



Manson's Method. -Have a perfectly clean cover-glass and slide. Touch the 

 apex of the exuding drop of blood with the cover-glass and drop it on the center of 

 the slide. The blood flows out in a film which exhibits an "empty zone" in the 

 center. Surrounding this we have the "zone of scattered corpuscles," next the 

 "single layer zone" and the "zone of rouleaux" at the periphery. It is well to ring 

 the preparation with vaseline. When desiring to demonstrate the flagellated bodies 

 in malaria, it is well to breathe on the cover-glass just prior to touching the drop of 

 blood. 



The Method of Ross is very easy of application and gives most satisfactory 

 preparations. Take a perfectly clean slide, and make a vaseline ring or square of 

 the size of the cover-glass. Then, having taken up the blood on the cover-glass, 

 drop it so that its margin rests on the vaseline ring. Gently pressing down the cover- 

 glass on the vaseline makes beautiful preparations which keep for a very long time. 

 If it is desired to study the action of stains on living cells, this method is also appli- 

 cable. A very practical way to do this is to tinge 0.85% salt solution containing i% 

 sodium citrate (the same as is used in opsonic work) with methylene azur, gentian 

 violet, or methyl green. With a Wright bulb pipette, take up one part of blood, 

 then one part of tinted salt solution. Mix them quickly on a slide and then deposit 

 a small drop of the mixture in the center of the vaseline ring and immediately apply 

 a cover-glass and press down the margins as before. This method will be found of 

 great practical value. 



A METHOD FOR MAKING DIFFERENTIAL LEUKOCYTE COUNT IN SAME 

 PREPARATION AS FOR WHLJE COUNT. 



Employ the same technic as in making the ordinary white count 

 but using as a diluting fluid a 2 % formalin solution to which has been 

 added one 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 +i. Of this 

 I use i 1/2% in a 1/2% 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 con- 

 tent of a cubic millimeter and then by 20 for the dilution. (Blood to 0.5; diluent 

 to IT.) 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 leuko- 

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

 hence the percentage of polymorphonuclears by this method is lower. 



