720 PROTOZOOLOGY 



cover from touching any part of the sUde, as this would cause the 

 water to run down into the depression. Nemeczek (1926) seems to 

 have been the first one who used the second coverglass for this prepa- 

 ration. If the Protozoa to be examined are large and observation can 

 be made under a low power objective, the small coverglass should 

 be omitted. 



As far as possible examine fresh preparations with low power ob- 

 jectives. The lower the magnification, the brighter and the larger the 

 field. The microscopical objects can quickly and easily be measured, 

 if an ocular micrometer division has been calculated in combination 

 with different objectives. 



For observation of cilia, flagella, extruded polar filament of Micro- 

 sporidia, etc., the so-called changeable condenser is useful, since it 

 gives both bright and dark fields under dry objectives. The ordinary 

 dark field condenser is used almost exclusively in conjunction with 

 an oil immersion objective and therefore for very active organisms 

 a great deal of time is often lost before satisfactory observation is 

 made. 



When treated with highly diluted solutions of certain dyes, living 

 Protozoa exhibit some of their organellae or inclusions stained with- 

 out apparent injury to the organisms. These vital stains are usually 

 prepared in absolute alcohol solutions. A small amount is uniformly 

 applied to the slide and allowed to dry, before water containing Pro- 

 tozoa is placed on it. Congo red (1 : 1,000) is used as an indicator, as 

 its red color of the salt changes blue in weak acids. Janus Green B 

 (1:10,000-20,000) stains chondriosomes. Methylene blue (1:10,000 

 or more) stains cytoplasmic granules, nucleus, cytoplasmic processes, 

 etc., Neutral red (1:3,000-30,000) is an indicator: yellowish red 

 (alkaline), cherry red (weak acid), and blue (strong acid). It also 

 stains nucleus slightly. Golgi bodies are studied in it, though its 

 specificity for this structure is not clear. 



Parasitic Protozoa should be studied in the tissue or body fluids in 

 which they occur. When they are too small in amount to make a 

 suitable preparation, one of the following solutions may bq used. 



Physiological salt solution. Widely used concentrations of NaCl 

 solutions are 0.5-0.7% for cold-blooded animals and 0.8-0.9% for 

 warm-blooded animals. 



Ringer's solution. The one Dobell advocated has been given al- 

 ready (p. 717). Another frequently used solution consists of 

 NaCl 0.8 gm. 



KCl 0.02 gm. 



CaCl2 0.02 gm. 



