COLLECTION, CULTIVATION, OBSERVATION 891 



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. 



The free-living ciliates swim about so actively as to make their 

 observation difficult. However, an actively swimming ciliate will 

 sooner or later come to stop upon coming in contact with various 

 debris, air bubbles or margin of the coverglass to allow a study of its 

 structure. Various reagents recommended for retardation of swim- 

 ming movements of ciliates, bring about deformities in the organisms 

 and therefore, must not be used; but a drop of saturated solution of 

 methyl cellulose may be added to a ciliate preparation to retard the 

 active movement of the organism without causing any visible ab- 

 normality (Marsland, 1943). 



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. The phase microscope is highly useful in studying various 

 intracellular structures in life. 



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 

 specific^ 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 be used. 



