418 HANDBOOK OF PROTOZOOLOGY 



to make an air-tight compartment. In turning over the whole, 

 in order to examine the preparation through the square cover- 

 glass, care must be taken to prevent the small circular cover- 

 glass from touching any part of the slide; for this would allow 

 the water to run down into the depression. In such a prepara- 

 tion, individual protozoans can be observed and studied for 

 several days without further treatment. 



The members of the Sarcodina give little trouble to an ob- 

 server, since they are not actively motile. To retard the active 

 movement of the Mastigophora and the Ciliata, various methods 

 have been advocated. Most of them, however, cause abnormal- 

 ity in form, structure, or behavior of the organisms, and should 

 be avoided as much as possible. Addition of a solution of picric 

 acid often will retard the movements of an actively mov- 

 ing protozoan without causing any deformity. When the 

 organisms are obtainable in large numbers some of them 

 may be stained on a plain slide by adding a drop of Lugol's 

 solution in order to bring out the number, location, or arrange- 

 ment of cilia, cirri, or flagella. Lugol's solution consists of 

 1 gm. of iodine, 5 gm. of potassium iodide, and 500 c.c. of 

 distilled water. 



Living protozoans, when treated with highly diluted watery 

 solutions of certain dyes, exhibit some of their parts stained 

 without being injured or killed by the treatment. Thisintra- 

 vitam staining is accomplished either by adding a drop of the 

 dye solution to the edge of the coverglass, or by allowing a 

 drop of the dye solution to dry on the slide before the water 

 containing the protozoans is added. Some of the dyes used 

 for this purpose are as follows: 



Auramin (1:2,000) to stain the nucleus. 



Bismarck brown (1:3,000 to 30,000) to stain the cytoplasm 

 yellowish and the granules reddish brown. 



Brilliant cresyl blue (1:10,000) to stain many granules in 

 the cytoplasm violet or blue. This dye frequently shows the 

 endosome of the nucleus. It may also be used for blood para- 

 sites such as trypanosomes, haemogregarines, etc. 



Congo red (1:1,000) to test the alkalinity and the presence 

 of organic acids (reddish color) and mineral acids (bluish). 



Methylene blue (1:10,000) to stain cytoplasmic granules. 



