88 MICROSCOPIC METHODS 



chamber at 120 C. for half an hour, (b) in a mixture of equal 

 parts of alcohol and ether for half an hour, then washed ^ and 

 dried, (c) in formol-alcohol (Gulland) (formalin 1 part, absolute 

 alcohol 9 parts) for five minutes, then washed and dried, or (d) 

 in a saturated solution of corrosive sublimate for two or three 

 minutes, then washed well in running water and dried. (Fig. 71 

 shows a film prepared by the last method.) In using the 

 Romanowsky stains no previous fixation is necessary (vide infra). 

 In the case of urine, the specimen must be allowed to stand, and 

 films made from any deposit which occurs ; or, what is still 

 better, the urine is centrifugalised, and films made from the 

 deposit which forms. After dried films are thus made from 

 urine it is an advantage to place a drop of distilled water on the 

 film and heat gently to dissolve the deposit of salts ; then wash 

 in water and dry. In this way a much clearer picture is 

 obtained when the preparation is stained. 



Within recent years it has become common to make blood 

 films on ordinary microscopic slides instead of upon cover- 

 glasses. Here the slides must be clean. This can be effected by 

 washing thoroughly first with weak alkali and then with water 

 and storing in alcohol. For use, a slide is taken from the 

 alcohol and the fluid adhering to it set on fire and allowed to 

 burn off, a dry clean slide being thus obtained. To make a film 

 on such, a small drop of blood is placed near one end, the edge 

 of a second clean slide is lowered through the drop on to the 

 surface of the glass on which the blood has been placed. This 

 second slide is held at an angle to the first, on which it rests by 

 its edge. The droplet of blood by capillarity spreads itself in 

 the angle between the two slides. The edge of the second slide is 

 then stroked along the surface of the first slide, and in this 

 procedure the blood is spread out in a film whose thickness can 

 be regulated by the angle formed by the second slide. Large- 

 sized films can thus be obtained, and when these are stained they 

 are often examined without any cover-glass being placed upon 

 them. A drop of cedar oil is placed on the preparation, and 

 after use this can be removed by the careful application of 

 xylol. 



Films dried and fixed by the above methods are now ready to 

 be stained by the methods to be described below. 



(b) Wet Method. If it is desired to examine the fine 

 histological structure of the cells of a discharge as well as to 

 investigate the bacteria present, it is advisable to substitute 

 " wet " films for the " dried " films, the preparation of which has 

 been described. The nuclear structure, mitotic figures, etc., are 



