coworkers (72, 73, 74) have described abnormalities of mitotic division occurring in cells cultured in the presence of mustard gas, iodoacetamide, and colchicine. Bacterial cells often assume abnormal and bizarre forms when grown in the presence of antiseptics and antibiotics (52, 142), some of which appear to interfere with the mechanism of bacterial division.
Preliminary observations on the action of various radiations have been reported (38, 82), and a detailed investigation of the action of ultraviolet and infrared rays on living cells is now in progress.
Concluding Remarks . Although no attempt has been made to survey the entire field of phase-contrast microscopy, it is hoped that this review will suffice to give the biologist some indication of what phase contrast sets out to do and how it does it. It is particularly important that all users of the method should have a thorough appreciation of its limitations in order that their results may be correctly interpreted. Phase contrast is such a great advance over older methods of studying cell structure that it provides a challenge to the cytologist, stimulating him to develop new and improved methods for preparing cells in a living and undamaged stage. Until this is done, many discussions concerning the structure of normal protoplasm are largely academic. We now have a system of microscopy which should encourage a much more critical approach to the study of the living cell than has hitherto been possible.
It was originally intended to give a list of the more important papers on the subject, as an appendix to this chapter, but this has now been rendered unnecessary as, coinciding with the completion of this section, an important new book on the subject has appeared. This is "Phase Microscopy," by A. H. Bennett, H. H. Osterberg Jupnik, and O. W. Richards , of the American Optical Company ( John Wiley & Sons, Inc., New York, N.Y.). Their work contains a complete bibliography of several hundred references up to 1950. It is interesting that the section on elementary theory is basically similar to the method used here except that the types of problem considered are different, and complex numbers are used instead of vector geometry and trigonometry. This book should be consulted by all serious students of microscopy.
Phase-contrast microscopy is essentially a method of microrefractometry, and any method which is capable of showing up differences in