BLOOD FILMS. 147 



equal to that described by Daniels. In this the drop of blood is drawn 

 along and not pushed. along. The films are even, can be made of any 

 desired thickness by changing the angle of the drawing slide, and there 

 is little liability of crushing pathological cells. Take a small drop of 

 blood on the end of a clean slide. Touch a second slide about 1/2 

 inch from end with the drop and as soon as the blood runs out along 

 the line of the slide end, slide it at an angle of 45 to the other end of 

 the horizontal slide. The blood is pulled or drawn behind the ad- 

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

 thinner film. One greater, a thicker film. 



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 

 preparation by this method. 



In the making of smears the chief points are to make the smear 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, Irishman's and other similar 

 stains the methyl-alcohol solvent causes the fixation. In staining 

 with Giemsa's stain, Ehrlich's tri-acid, haematoxylin and eosin, 

 Smith's formol fuchsin, and with thionin, separate fixation is necessary. 

 For Giemsa and thionin, either alcohol and ether (15 minutes), ab- 

 solute alcohol (10 to 15 minutes) or methyl alcohol (2 to 5 minutes) 

 answer well. 



Formalin vapor, for 5 to 10 seconds, is also used for fixation. For 

 Ehrlich's tri-acid, haematoxylin 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 



