FILM PREPARA TIONS. 85 



For use, a cover-glass is either dried by wiping with a clean 

 duster or is simply allowed to dry. This method will 

 amply repay the trouble, and really saves time in the end. 

 A clean cover having been obtained, the film preparation can 

 now be made. If a fluid is to be examined a loopful may be 

 placed on the cover-glass, and either spread out over the 

 surface with the needle, or another clean cover may be 

 placed on the top of the first, the drop thus spread out 

 between them and the two then drawn apart. When a 

 culture on a solid medium is to be examined a loopful of 

 distilled water is placed on the cover-glass and a minute 

 particle of growth rubbed up in it and spread all over the 

 glass. The great mistake made by beginners is to take 

 too much of the growth. The point of the straight needle 

 should just touch the surface of the culture, and when this 

 is rubbed up in the droplet of water and the film dried, 

 there should be an opaque cloud just visible on the cover- 

 glass. When the film has been spread it must next be 

 dried by being waved backwards and forwards at aim's- 

 length above a Bunsen flame on the worker's bench. The 

 film must then be fixed on the glass by being passed three or 

 four times slowly through the flame. In doing this a good 

 plan is to hold the cover-glass between the right forefinger 

 and thumb ; if the fingers just escape being burned no 

 harm will accrue to the bacteria in the film. 



In making films of a thick fluid such as flus it is best 

 to spread it out on one cover with the needle. The result 

 will be a film of irregular thickness, but sufficiently thin at 

 many parts for proper examination. Scrapings of organs are 

 very convenient if only the presence or absence of organisms 

 is inquired after. Such scrapings may be smeared directly 

 on the cover-glasses with or without the addition of sterile 

 distilled water. 



In the case of blood, a fairly large drop should be 

 allowed to spread itself between two cover -glasses, which 

 are then to be slipped apart, and being held between the 

 forefinger and thumb are to be dried by a rapid to-and-fro 

 movement in the air. A film prepared in this way may be 



