48 PATHOGENIC BACTERIA 



drop, with few exceptions, is the best ; the important method of 

 Gram, for instance, cannot be carried out except on a dry prep- 

 aration. 



The Dry Method. The more minute attention paid to de- 

 tails, the more satisfactory will be the results. 



To commence with, then, the cover-glasses (No. 1 thick- 

 ness) must be properly clean. They are to be moved about in a 

 capsule or other flat vessel of hydrochloric acid, washed in com- 

 mon water and then kept in a wide-mouthed stoppered bottle of 

 absolute alcohol, to which glacial acetic acid has been added in 

 the proportion of 10 per cent. The addition of acid will be 

 found to prevent the cover-glasses receiving too high a polish 

 when wiped, a result which greatly interferes with the equable 

 distribution of the bacteria over the surface. Three cover-glasses 

 having been wiped dry, a loop of distilled water is placed on 

 each ; the loop should be drawn a short way over the surface, 

 and if it is found that the water does not adhere to the glass, 

 but returns again to a bead, the cover must be replaced in the 

 acidulated alcohol and wiped afresh. The sterilized loop having 

 been inserted into the culture tube and a small quantity of the 

 growing edge withdrawn, it is applied to the drops of water in 

 succession, and the residue having been burned off in the flame, 

 the loop is used to distribute the turbid drop over the entire 

 face of each of the cover-glasses, which are then allowed to dry; 

 the distribution is facilitated by breathing on the surface, and 

 the glasses are best steadied by the pressure of a needle. The 

 prepared side is to be kept upwards throughout all the subse- 

 quent manipulations. The time-honored custom is now to pass 

 the covers thrice across the flame, with the object of coagulating 

 the albumen and fixing the films. Although so generally 



