186 THE TECHNICS OF PHASE MICROSCOPY 



densiphase contrast present can be added to the color contrast for 

 increased differential visibility. Dispersion staining is useful with 

 colorless, or nearly so, specimens for bringing out detail and for evaluat- 

 ing impurities or contaminants within the specimen (see Section 2 of 

 Chapter Yl). Dispersion often explains the colors seen in some un- 

 colored specimens under the phase microscope. The microscopist 

 should be familiar with color theory and with the limited sensitivity 

 of his own eye to avoid errors of interpretation when microscopy involves 

 color (Evans, 1948). 



3.6. Photomicrography 



Photographic records are as easily made with the phase microscope 

 by following the same rules and methods as in other photographic 

 procedures. Nearly all the published papers on phase microscopy are 

 illustrated with photomicrographs which attest this statement. Color 

 may be recorded with color films when it is a part of the record. 



The ability to see details and to follow physiological processes hitherto 

 invisible in living organisms early brought out the value of making 

 records with the motion picture camera. Grasshopper spermatogenesis 

 was recorded in dark (A — ) contrast in a notable film by Michel (1941, 

 1950). Harrison et al. (1946) filmed the serological reactions of a green 

 and a colorless species of Paramecium bvrsaria with Anscocolor motion 

 picture film; color was important as a natural marker indicating the 

 sensitized animals. In England, Hughes and his associates have filmed 

 mitosis and have also combined phase and polarization microscopy for 

 motion picture analyses of dividing cells (Hughes and Fell, 1949; 

 Hughes and Preston, 1949, and Hughes and Swann, 1948). A phase 

 motion picture of tumor cells was produced by Dr. G. 0. Gey (Firor and 

 Gey, 1947), and a tissue culture film of salamander lung cells was made 

 by Danes (1949). Farris (1947-1950) has made motion pictures of 

 vertebrate spermatozoa. Films showing the growth and life histories 

 of fungi should be available, and with long-focus methods that permit the 

 use of normal cultures in Petri dishes they could be made under normal 

 conditions of growth (Richards, 1947a, 19486). 



The phase microscope replaces the brightfield microscope, or phase 

 accessories may be added to existing equipment. The slightly longer 

 exposures are usually not a serious handicap as a 100-watt lamp has been 

 found more than adequate for color film. Various kinds of equipment 

 for this work are described in the Journal of the Biological Photographic 

 Association (see the Cumulative Index 17: 192, 1949; also Dragesco, 

 1948; Heard, 1932; and Richards, 1934). Hughes (1949) discusses 



