COLLECTION, CULTIVATION, OBSERVATION 899 



Fontana's method. For staining filamentous structures such as the 

 extruded polar filament of microsporidian spores, this method is the 

 most satisfactory one. After air-drying the smears are fixed for 5 

 minutes in a mixture of formaldehyde, 20 cc; glacial acetic acid, 1 

 cc; and distilled water, 100 cc. After washing in running water, the 

 smears are placed in the following mordant composed of equal parts 

 of 5 per cent tannic acid and 1 per cent carbolic acid, for about 2 

 minutes at about 60°C. Wash the smears in water and place them for 

 3-5 minutes in 0.25 per cent solution of silver nitrate warmed to 

 60°C, to which ammonia has been added drop by drop until a gray- 

 ish brown cloud appeared. Wash thoroughly and air-dry. After pass- 

 ing through 95 per cent and absolute alcohol, and xylol, the smears 

 are mounted in Canada balsam 



b. Blood film preparations 



Thin film. The finger tip or ear lobe is cleaned with 70% alcohol. 

 Prick it with an aseptic blood lancet or a sterilized needle. Wipe off 

 the first drop with gauze and receive the second drop on a clean slide 

 about half an inch from one end (Fig. 376, 1). Use care not to let the 

 slide touch the finger or ear-lobe itself. Quickly bring a second slide, 

 one corner of which had been cut away, to the inner margin of the 

 blood drop (1), and let the blood spread along the edge of the second 

 slide. Next push the second slide over the surface of the first slide at 

 an angle of about 45° toward the other end (#). Thus a thin film of 

 blood is spread over the slide (3). Let the slide lie horizontally and 

 dry, under a cover to prevent dust particles falling on it and to keep 

 away flies or other insects. If properly made, the film is made up of 

 a single layer of blood cells. 



Thick films. Often parasites are so few that to find them in a thin 

 film involves a great deal of time. In such cases, a thick film is advo- 

 cated. For this, 2 to 4 drops of blood are placed in the central half- 

 inch square area, and spread them into an even layer with a needle 

 or with a corner of a slide. Let the film dry. With a little practice, a 

 satisfactory thick smear can be made. It will take two hours or more 

 to dry. Do not dry by heat, but placing it in an incubator at 37°C. 

 will hasten the drying. When thoroughly dry, immerse it in water 

 and dehaemoglobinize it. Air dry again. 



Thin and thick film. Often it is time-saving if thin and thick films 

 are made on a single slide. Place a single drop of blood near the center 

 and make a thin film of it toward one end of the slide. Make a small 

 thick smear in the center of the other half of the slide. Dry. When 



