FILM PREPARATIONS 95 



Slides and cover-glasses may be cleaned by boiling them 

 in a porcelain dish with 10 per cent, carbonate of soda 

 solution for a few minutes, well washing, and then treating 

 with strong sulphuric acid, warmed carefully in a porcelain 

 dish, for a few minutes. The acid having been poured off, 

 they are well rinsed in several changes of water, and 

 should be kept in a stoppered glass pot or capsule in 

 absolute alcohol. 



A clean slide (or cover- glass) is taken, dried with a 

 clean soft linen or silk rag or handkerchief, or with 

 Japanese paper, or it may be momentarily introduced into 

 the Bunsen flame and the spirit burnt off, and placed 

 flat on a convenient support on the work-table a white 

 glazed tile is excellent with the end or corner projecting 

 so that it can be conveniently picked up. 1 A droplet 

 (i.e. small drop) of tap-water or of physiological salt 

 solution (not distilled water) is then placed on it, in the 

 middle, by means of a looped platinum needle, or with 

 a small glass pipette (Fig. 7). Theoretically, physiological 

 salt solution 2 sterilised by boiling should be used, but 

 ordinary tap- water may generally be employed. A thin 

 film of organisms has now to be formed on the glass, and 

 the following is the method of procedure with a culture 

 on a solid medium such as agar or gelatin. The culture 

 tube and platinum needle are held and manipulated in 

 precisely the same manner as that described for the 

 inoculation of tubes (p. 69). 



A mere trace of the growth from a culture should be 

 taken, just sufficient to soil the tip of the straight platinum 

 needle, or the preparation will be too crowded, and this 

 is well rubbed up with the droplet of water on the glass, 



1 The writer has devised a useful support for staining. It consists 

 of a square of plate glass, painted half white and half black at the 

 back, and having a narrow strip of thick glass cemented across it on 

 which the gl":js rests. It is made by Messrs. Baird and Tatlock. 



2 0-75-0-95 per cent, of sodium chloride dissolved in distilled water. 



