206 MICROMETRY AND BLOOD PREPARATIONS 



piece of linen. As the accuracy of the counting chamber depends upon the integrity 

 of the cement, any reagent such as alcohol, xylol, etc., and, in particular, heat, will 

 ruin the instrument. The pipettes should be cleaned by inserting the ends into the 

 tube from a vacuum pump, as a Chapman pump. First draw water or i% sod. 

 carbonate solution through the pipette, then alcohol, then ether, and finally allow 

 air to pass through to dry the interior. If the interior is stained, use i% HC1 in 

 alcohol. If a vacuum pump is not at hand, a bicycle pump or suction by mouth 

 will answer. 



PREPARATIONS FOR THE STUDY OF FRESH BLOOD 



Many authorities prefer a fresh-blood specimen to a stained dried 

 smear in the study of parasites of the blood. In malaria in particular 

 there is so much information as to species to be obtained from a fresh 

 specimen that the employment of this method should never be neglected. 

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

 could not be better spent than 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 i part of blood, 

 then i 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 WHITE COUNT 



Employ the same technic as in making the ordinary white count 

 but using as a diluting fluid a ij^ or 2% formalin solution to which has 



