The Microscope. 155 



finger is pricked with a pin that has been heated to redness, and 

 allowed to cool, the little round globule of blood that appears i& 

 touched with a clean slide ; a cover glass is lowered down on to 

 the blood, which is pressed out until the film assumes a trans- 

 parent yellow color ; the film is then not too thick, and should 

 be examined at once. The clot that is formed at the margin 

 prevents the drying of the film ; but, in order to keep the film 

 thin, it is better to wipe away the blood that is prossed from 

 under the cover glass, and then to surround with parrafin. Day- 

 light and no sub-stage condenser should be used for examinations,, 

 or the organisms are rendered too transparent The movements 

 of the flagella and the amoeboid movements can all be made out. 

 If the organisms are pigmented they are readily enough seen, 

 but a most careful search may have to be made for those non- 

 pigmented organisms that sometimes adhere to the red blood 

 corpuscles. If the specimen is to be preserved for further ex- 

 amination the film should be prepared by compressing between 

 two cover glasses, which are carefully separated, allowed to dry,, 

 and passed two or three times through a clear flame; each film 

 is mounted unstained and dry, with a parrafin rim to keep out 

 the air, and to retain the cover glasses in position. When it is 

 wished to stain the organisms in order to bring them into special 

 prominence, the films, after being heated on the cover glass, are 

 put into a mixture of alcohol and ether, they are then allowed 

 to dry, after which they are stained with a concentrated aqueous 

 solution of methylene blue for thirty seconds; they are then 

 rinsed in water and mounted dry, the cover glass being sur- 

 rounded with parrafin. The leucocytes are colored deep blue, 

 the free spherical organisms and those adhering to the red blood 

 corpuscles pale blue, whilst other forms are scarcely tinged. A 

 contrast stain may be obtained by using eosin. With these 

 stained preparations artificial light may of cpurse be used. In 

 all cases where possible, both methods of preparation should be 

 resorted to, as each has its advantages. — Brit. Med. Jour. 



