BACTERIA, PHAGE, AND VIRUS 



199 



* Richards, unpublished observations. 



t Commercial designations: IB— 0.25X = low B— contrast. 2.5B— 0.25X = 

 medium B— contrast. Of the A+ and the A— plates 0.07 is high contrast, 0.14 

 is medium contrast, and 0.2 is low contrast. The A— gives dark and the \+ bright 

 contrast for specimens with greater optical path than that of their suiround. 



phase (a = 0.07 and 0.05 /x). The results agree with theory in that the 

 same value was obtained with both contrasts within the error of measure- 

 ment. The relation of these values to those in the literature are dis- 

 cussed in the original paper, although direct comparison was not possible 

 since other methods (even negative staining) alter the size of the 

 bacterium and bright field microscopy does not provide an image sharp 

 enough for measurement. The use of phase microscopy and motion 

 picture recording should clarify some problems of growing bacteria 

 and disputed life histories (Section 3.6 of Chapter IV). 



Unstained bacteria show considerable detail (Fig. V.l). The outside 

 wall does not show in most living, unstained organisms. With stained, 

 mordanted B. cereus the 0.14A— 0.25X diffraction plate shows both wall 

 and detail (Fig. Y.2E). Unmordanted stained cells (Fig. V.2F) show 

 nuclear detail as dark areas with a 0.15A+0.25X plate. We are in- 

 debted to Dr. Robinow for the preparations from which Figures Y.2E 

 and Y.2F were made. Increased contrast from reversal to bright 

 contrast by means of a 0.07A-|-X/4 plate and red light from a Wratten A 

 filter may be obtained with Ziehl-Neelsen stained bacteria (Fig. V.2, 

 A-D). The limitations of this procedure were discussed in Section 3.5 

 of Chapter IV. Septa were observed at each full turn of the spiral in a 

 giant spirochete by Dyar (1947) (Fig. V.l/v). Leprosy bacteria have 

 been studied with phase by Hichards and Wade (1949). Haselmann 



