212 PHASE MICROSCOPY IN BIOLOGY AND MEDICINE 



examination of mesoderm formation in the guinea pig. Photographic 

 records of the development of nerve cells of the 5-day chick embryo were 

 made by S. C. Williams (1949a, h) over a 2-week period. 



6.2. Histology 



The epithelial cells of the tongue and the inner lining of the cheek have 

 been the regular test object for phase microscopy because of their un- 

 limited availability and ease of preparation. Almost all the earlier 

 papers have pictured them, either with or without bacteria, but owing 

 to the differences in the reproductions (screen and paper quality) it is 

 not possible to compare the efficiencies of the various methods from the 

 published illustrations (see Section 4 of Chapter V). Richards (1944) 

 examined the epithelium from the nictitating membrane of the frog, 

 which is easily prepared and offers more detail than the squamous epi- 

 thelial cells from the mouth. Improved resolution with ultraviolet phase 

 microscopy was demonstrated by Bennett et al. (1948). Chase and 

 Smith (1949) reported the B— dark contrast valuable for study of pig- 

 ment in hair. Zahn and Haselmann (1950) have examined the middle 

 membrane in hair. 



Frauchiger (1940) examined the choroid plexus in Tyrode's solution 

 and concluded that the phase microscope should be useful in neurology 

 and, with toluidin blue, should help to explain the function of the 

 plexus. Brain tissue of several animals was studied by Hoessley (1947) 

 with brightfield, phase, and ultramicroscopy. He believed that all the 

 methods would provide new conclusions. A structure was reported to 

 appear after death that resembled the Nissl body and might be a pre- 

 cursor of it. Fixation changes were also investigated. Gatenby and 

 Moussa (1949) have examined dorsal root ganglion cells, and Peters et 

 al. (1950) have studied dendrites. Thomas (1947) described a beaded 

 appearance observed in the motoneurones of Helix that was distiu'bed 

 on fixation and found very small granules which he proposes calling 

 microneurosomes. He believes that one of the prime advantages of the 

 phase microscope is the revelation of smaller granules than can be seen 

 with other microscopical methods. S. C. Williams (1949a, b) followed 

 nerve-cell development of chick embryo tissue. (See also Section 6.1.) 

 The islet tissue of Langerhans has been examined by Hartroft (1950). 



The middle and Krause's membranes of unstained muscle fibers were 

 seen by Albertini (194G6), and Ralph (1949) has photographed even 

 smaller details within the muscle cell with the phase microscope. Con- 

 nective tissue was examined early in the history of phase microscopy by 

 Loos (1941a). A diffraction plate of greater contrast (O.IA — 0.25X) 

 shows the elastic and gelatin-containing fibers better than the usual 



