54 BACTERIOLOGY 



(d) Place for a few seconds in a 0.25 to 0.50 per cent solution of 

 nitrate of silver — "the sensitizing bath." 



(e) Without washing transfer to the "reducing and reinforcing 

 bath": 



Gallic acid , . . . 5 grams. 



Tannic acid 3 grams. 



Fused potassium acetate lo grams. 



Distilled water 350 c.c. 



(/■) After a few seconds, replace the preparation in the nitrate 

 of silver solution, in which it is kept constantly moving, tUl the 

 solution begins to acquire a brown or black color. 



(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 solution 

 of mercuric chloride, 100 c.c, with absolute alcohol, 50 c.c, 

 and acetic acid, 5 drops. After a few minutes the preparation 

 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. 



Heidenhain'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 hematoxylin 



