EMBRYOLOGY 211 



Formalin, especially neutral or alkaline (10%), was better, and the Zen- 

 ker-formol-osmic fluids gave fixed images resembling the living cell most 

 closely. Hoessley (1947) investigated killing agents. Chromosome 

 changes with fixation were described by Schultz (1947). 



Oliver (1948) watched the fixation of isolated cells and reported a 

 sharpening of detail in the structure as the protoplasmic elements became 

 denatured. He also stated that ". . . it can be definitely ol)served while 

 the process is occurring under the eye that no structures similar to rods 

 or droplets result as artifacts or products of fixation ..." with weak 

 formalin treatment. Barer (19486) shows photomicrographs of living 

 and fixed salamander testis. Crawford and Barer (1949) used formalin 

 fixation of li^'ing, teased cells from Salamandra niacidosa and reported 

 shrinkage first, followed by swelling and exudation of bubbles. The 

 addition of saline reduced the swelling. Whether the same condition 

 prevails in blocks of tissue is imcertain. Detailed studies on cellular 

 death were reported by Zollinger (1948(/). (See also Peters et al., 1950.) 



Haselmann (19486) believes that better detail can be seen in fibrils 

 and membranes with the phase microscope after staining. This, he 

 states, may be due to luminescence, refraction, or total absorption of 

 the dye. Observations with diffraction plates other than those available 

 in the Zeiss equipment should clarify these relations. With very small 

 specimens, as with bacteria, staining procedures, especially metal im- 

 pregnation methods, increase the size of the organism and may make 

 observation possible with the light microscope. Combined fixing, stain- 

 ing, and mounting media (Zirkle, 1940) should be tried both with and 

 without the stain. 



6. EMBRYOLOGY AND HISTOLOGY 

 6.1. Embryology 



The structures of spermatozoa, usually re\'ealed by staining, may be 

 seen in unstained living cells with the phase microscope. Study of 

 motion and counting may be done to advantage with medium bright 

 contrast, and structure may be observed with dark contrast. Farris 

 (1947, 1948n, h) has made motion pictures of normal and atypical sperm 

 and their locomotion which provide basic information for alleviating 

 human infertility. An early sperm phase photomicrograph is to be 

 found in Smith (1946). 



Fertilization and early development of the rat has been studied by 

 Austin and Smiles (1948) and by Odor and Blandau (1949). At the 

 1949 meeting of the American Association of Anatomists, Odor and 

 Blandau exhibited remarkable photographs showing the sperm within 

 the egg. Albertini (1947) reported phase microscopy helpful in the 



