54 BACTERIOLOGY 



(g) Finally wash in distilled water, dry, mount in Canada 

 balsam. It is difficult to avoid the formation of precipitates; 

 otherwise the results of this method are usually good. 



Wet Fixation of Protozoa. The fluid containing the protozoa 

 is spread on a cover-glass or slide and immediately dropped upon 

 a solution of the fixing agent, commonly sublimate alcohol heated 

 to 60 C. This is prepared by mixing saturated aqueous solu- 

 tion of mercuric chloride, 100 c.c., with absolute alcohol, 

 50 c.c., and acetic acid, 5 drops. After a few minutes the prepa- 

 ration is carefully washed in water, and passed through graded 

 alcohols to harden. It may then be stained, dehydrated in 

 graded alcohols, cleared in xylol and mounted in balsam. The 

 preparation should not be allowed to dry at any stage of the 

 process. 



Haidenhain's Iron Hematoxylin. The preparation to be 

 stained by this method should be fixed in mercuric chloride or 

 alcohol. The stain is prepared by dissolving hematoxylin crys- 

 tals, i gram, in hot absolute alcohol 10 c.c., and then adding dis- 

 tilled water 90 c.c. This solution is allowed to stand in an open, 

 cotton-plugged bottle for about four weeks, and it is then diluted 

 with an equal volume of water before using. The iron solution 

 is made by dissolving 2.5 grams of ferric ammonium sulphate 

 (lavender-colored crystals) in 100 c.c. of distilled water. The 

 preparation to be stained is first soaked in the iron solution 

 for four to eight hours, then rinsed and immersed in the hema- 

 toxylin for twelve to twenty-four hours. It is again rinsed and 

 now differentiated by immersion in the iron solution until black 

 clouds cease to be given off. When the desired differentia- 

 tion has been obtained the preparation is washed, dehydrated 

 by passing through graded alcohols, and absolute alcohol, cleared 

 in xylol and mounted in balsam. 



Preparation and Staining of Blood Films. Blood films are 

 best made on clean, flamed slides. A small drop of fresh blood is 

 received on the surface of one slide near one end. The end of 

 another slide is applied to the first at an acute angle so that the 



