METHOD OF PREPARING AND EXAMINING THICK-FILMS 355 



the surface of the slide ; or one can spread the drop with the 

 sticking needle or corner of the labeled end of the next slide. 

 Put on a large drop, three or four times as much as one would 

 use for a thin film, and spread it over an area of from one to 

 one and one-half centimeters in diameter. It does not matter if 

 the blood is thicker in some parts of the film, and a good deal 

 of latitude is permissible in the amount of blood used; but one 

 should avoid the not uncommon error of using a very small 

 amount of blood and then spreading it so much that it becomes 

 the equivalent of a thin film. If the slide is subsequently to be 

 stained in the upright position, place the thick drop with its 

 lower margin about one-half centimeter from the end of the slide, 

 else a good deal of stain will be required to cover the specimens. 



Labels may be written with a wax pencil on the unused end of 

 the slide. It is often convenient to number a batch of slides be- 

 forehand. Each batch should be marked with a distinguishing 

 letter or other symbol as well as numbered. 



As soon as the blood is spread, place the slide in a box where 

 it will be protected from dust. Keep the box upright until the 

 blood has dried enough so that it will not run. While the box is 

 being filled it may be fastened with a strong rubber band to a 

 block or other convenient support in order to prevent accidental 

 tipping. (Fig. 20, A). Such a support may be made of two blocks 

 of soft wood, fastened to each other at a right angle, the up- 

 right block being three and one-half inches wide, one inch thick, 

 and about six inches long. The horizontal block should be three 

 and one-half inches wide, two inches thick and about four inches 

 long. 



Drying fdms. Thick films should be dried enough to make them 

 adhere during the staining, but too much drying will prevent a 

 clear staining of the parasites. 



In ordinary summer weather preparations will dry enough to 

 stick well if kept overnight in boxes with closed lids. Or, the lids 

 may be removed and the shdes dried from one to one and one-half 

 hours in an incubator. When preparations are to be sent some 

 distance by mail before staining, or when it is impractical for any 

 reason to stain soon after taking them, they may be protected 

 from overdrying for some days by wrapping them in paraffined 

 paper. In any case, they must be protected from flies and cock- 

 roaches, which will eat dried films, and from dust. The tempera- 



