FILM PREPARATIONS. 97 



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. 



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 

 " corrosive " films for the " dried " films, the preparation of 

 which has been described. The initial stages in the pre- 

 paration 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 placed in 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 

 fixing solution, by saturating the 25 c.c. of alcohol with 

 7 



