METHODS OF STAINING BLOOD 277 



the blood is obtained by pricking it. The first drop having 

 been wiped away with a sterilised platinum needle, the 

 second is taken off with a disinfected cover-glass, spread 

 out by rubbing with another cover-glass (also disinfected), 

 dried, and heated to 120 0. approximately. Disinfection 

 of the cover-glasses is best done in corrosive sublimate, 

 from which they are transferred to alcohol and ether with 

 a sterilised forceps, and then taken out and rapidly dried 

 in the air. The basic aniline dyes, commonly used for 

 bacteriological examination, are employed in aqueous solu- 

 tions, with the occasional addition of alcohol, glycerine, or 

 acetic acid to the fluid. The stains are allowed to act for 

 some minutes and then rinsed off with distilled water ; the 

 preparation is dried and Canada balsam applied to it, or if 

 it is not wished to keep the specimen for any length of time, 

 it is mounted temporarily in oil of cloves, origanum, or 

 cedar. Loffler's alkaline solution of methyl blue [pp. 86, 

 241], and Gram's method with its modifications (p. 76), are 

 also much used. 



According to Giinther's method, the preparations of 

 blood after being dried and fixed are rinsed in dilute solution 

 of acetic acid (1 to 5 per cent.), by which means the 

 haemoglobin is extracted from the corpuscles and a great 

 part of the plasma washed from the glass, without thereby 

 impairing the adhesion of the bacteria. If now the sections 

 are again dried they may be stained after the ordinary 

 methods, and a tolerably isolated coloration of the bacteria 

 so effected. The blood-corpuscles are no longer seen save 

 as mere shadows, and do not now interfere with the appear- 

 ance of the stained bacteria. 



The rinsing away of the plasma with acetic acid does 

 not succeed if the layer of blood be already too long dried 

 upon the cover-glass. Giinther accordingly treats dried-up 

 layers with a 2 to 5 per cent, aqueous solution of pepsine, 



