86 MICROSCOPIC METHODS. 



too thick at one edge, but at the other is beautifully thin. 

 If it is desired to preserve the red blood-corpuscles in such 

 a film it must be fixed by being placed in a hot-air chamber 

 at 120 C. for half an hour, or in a saturated solution of 

 corrosive sublimate for two or three minutes, then washed 

 and dried. (Fig. 55 shows a film prepared by the latter 

 method.) 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. Films dried and 

 fixed by the above methods are now ready to be stained 

 by the methods to be described below. 



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 " corrosive " 

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

 been described. The initial stages in the preparation of 

 corrosive films are the same as for other films, but instead 

 of being dried in air they are placed, while still wet, film 

 downwards on a saturated solution of perchloride of 

 mercury in .75 per cent sodium chloride, in which they are 

 allowed to remain for five minutes. They are then placed 

 for half an hour, with occasional gentle shaking, in .75 per 

 cent sodium chloride solution to wash out the corrosive 

 sublimate. They are then passed through successive 

 strengths of methylated spirit, being allowed to remain a 

 few minutes in each. After this treatment they are stained 

 and treated as if they were sections. The nuclear structure, 

 mitotic figures, etc., are by this method well preserved, 

 whereas these are considerably distorted in dried films. 



Another excellent method of fixing film preparations is 

 that devised by Gulland. The fixing solution has the 

 composition absolute alcohol, 25 c.c., pure ether, 25 c.c., 

 alcoholic solution of corrosive sublimate (2 grm. in 10 c.c. 

 of alcohol), about 5 drops. The films are placed, while 

 still wet, in this solution for five minutes or longer. They 

 are then washed well in water, and are ready for staining. 

 A contrast stain can be applied at the same time as the 



