BLOOD SMEARS l8l 



horizontal slide. The blood is pulled or drawn behind the advancing 

 edge of the advancing slide. An angle less than 45 makes a thinner 

 film; one greater, a thicker film. 



Instead of a slide a square cover-glass may be used and if the edge be smooth it 

 makes a more satisfactory spreader than the slide. Many workers prefer the Ross 

 thick-film method in examining for malaria. In this about one-half of a drop of 

 blood is smeared out over a surface about equal to that of a square cover-glass and 

 allowed to dry. It is then flooded with a 0.1% aqueous solution of eosin for 

 about 15 minutes. The preparation is then gently washed with water and then 

 treated with a polychrome methylene-blue solution. After a few seconds this is 

 carefully washed off and the preparation dried and examined. 



Instead of the Daniels method some prefer to take up the drop of blood on the 

 slide on which the smear is to be made, about 1/2 inch from the end. Then apply 

 the spreader slide and so soon as the drop runs along the end of the spreader slide 

 proceed as above described. 



Of the various methods of making smears by means of cigarette paper, rubber 

 tissue, needles, etc., the best seems to be to take a piece of capillary glass tubing and 

 use this instead of a needle in making the film. There is one advantage about the 

 strip of cigarette paper touched to the drop of blood and drawn out along the slide 

 or cover-glass, and that is that it is almost impossible not to make a working prepa- 

 ration by this method. 



In the making of smears the chief points are to make the smears as 

 soon after taking the blood as possible and to have slides and cover- 

 glasses scrupulously clean. It is well to flame all slides and cover- 

 glasses which are to be used for blood-work. This is the best method 

 of getting rid of grease. 



Fixation of Film. In Wright's, Leishman's, and other similar stains the methyl- 

 alcohol solvent causes the fixation. In staining with Giemsa's stain, Ehrlich's 

 tri-acid, hsemotoxylin and eosin, Smith's formol fuchsin, and with thionin, separate 

 fixation is necessary. For Giemsa and thionin, either absolute alcohol (ten to 

 fifteen minutes), or methyl alcohol (two to five minutes) answer well. 



Formalin vapor, for five to ten seconds, is also used for fixation. For Ehrlich's 

 tri-acid, haemotoxylin and eosin and formol fuchsin, heat gives the best results. 

 The best method is to place the films in an oven provided with a thermometer. 

 Raise the temperature of the oven to 135 C. and then remove the burner. After 

 the oven has cooled, take out the fixed slides or slips. 



Some prefer to place a crystal of urea on the slide, then hold it over the flame 

 until the urea melts. This shows that a temperature between 130 and 135 C. has 

 been reached. 



One of the handiest methods is to drop a few drops of 95% alcohol on the slide 

 or cover-glass. Allow this to flow over the entire surface; then get rid of the excess 

 of alcohol by touching the edge to a piece of filter-paper for a second or two. Then 

 light the remaining alcohol film from the flame and allow the burning alcohol to 

 burn itself out. A chemical fixation which gives good fixation for haematoxylin 



