New developments in microscopy and electrophysiology have brought a renewal of interest in methods of micromanipulation. A number of features desirable in the design of a micromanipulator is discussed. A new micromanipulator is described. Its outstanding features are (1) single control; (2) massive construction with freedom from vibration; (3) freedom from play; (4) continuous variability of sensitivity; (5) limitation of range of movement to the field of view; (6) rapid low-power centring; (7) unusual robustness combined with delicacy of movement achieved without any high-precision methods. The performance of the instrument is adequate for high-power cytological work and for microdissection by phase-contrast illumination.
Some extensions of the simple theory of phase-contrast microscopy are considered. It is emphasized that transparency , rather than thickness , is the limiting factor for the successful employment of the method. Certain transparent insect larvae ( Chaoborus, Chironomus ) can be observed in the living state by phase-contrast illumination. The statement that the method is of no value for the examination of fixed and stained sections is based on consideration of an ideal physical case. In practice the method may be a valuable adjunct to routine examination of such material. Examples are given of the application of phase-contrast microscopy to normal and pathological stained sections.