FRESH BLOOD FILMS. 145 



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 ne- 

 glected. While waiting for the film to stain one has 5 or 6 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 prepara- 

 tion with vaselin. 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 

 vaselin 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 vaselin ring. Gently pressing down the cover-glass on the vase- 

 lin makes beautiful preparations w r hich keep for a very long time. If 

 it is desired to study the action of stains on living cells, this method is 

 also applicable. A very practical way to do this is to tinge .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 vaselin ring and immediately 

 apply a cover-glass and press down the margins as before. This method 

 will be found of great practical value. 



