OTHER FUNGI 203 



How small a virus particle may be seen depends on its path difference. 

 For the Rhizohium phage better visibility was obtained with less re- 

 tardation of a 0.17A+0.1\ diffraction plate, and other than the quarter- 

 wave retardations should be tried with these materials. The possibil- 

 ities of examining objects below the limit of resolution with the phase 

 microscope, as discussed by Osterberg (19476), offer promise. Also, 

 with bright contrast the intensity of the light alone determines the 

 smallness of particle that may be detected. Whene\'er the center of the 

 diffraction pattern is bright enough to stimulate the receptor, it will be 

 discovered. 



Haselmann and Kappel (1949) recommend a high-aperture N.A. 1.4 

 phase objective for the study of living gonococci. Nuclear changes in 

 Rhodomicrobhim have been described by Murray and Douglas (1950). 

 Tulasne (1949) is investigating nuclear and cytological detail in the 

 division of bacterial cells. Even with such small cells the phase micro- 

 scope is aiding in the understanding of living processes. These possi- 

 bilities of the phase microscope should be explored by the bacteriologist 

 and virologist. 



3.2. Other fungi 



The larger filamentous fungi may be seen with low-contrast phase 

 objectives (0.2Ad=0.25X), and the smaller Actinomycetes can be seen 

 with high contrast (0.07A±0.25X). Petri dish cultures may be observed 

 with a long-focus phase condenser (Fig. V.3, C-H, and M). A cover 

 glass should be placed over the area to be obser\'ed with the higher 

 power objectives; otherwise the moisture collecting on the lens obscures 

 the detail. Spores and spore formation show well with phase micros- 

 copy. A B— diffraction plate shows more detail w^ithin the mycelium, 

 and it is preferable for pigmented fungi. Unless the pigmentation is 

 very dense, more detail will be seen with phase than with brightfield 

 microscopy. 



Yeasts and yeast-like organisms show better with medium to high 

 bright-contrast and with 2.5B— 0.25X dark-contrast phase (Fig. V.3, 

 J-L). The B— permits focusing through the cell and seeing the 



Fig. v.3. Fungi and viral inclusion bodies. A, B, Ashbya gossypii, brightfield fails 

 to show the flagellum clearly seen with liright-contrast phase, 1000 X. C-E, Hortno- 

 dendron, and F-H, Monilia, growing on agar in a Petri dish, 67 X : C, F, brightfield; 

 E, G, high dark-contrast (B — ) phase. D, H, bright-contrast phase. J-L, yeast, 

 700 X: J, medium dark-contrast (B — ) phase. K, dark-contrast (A — ) phase. 

 L, bright-contrast phase. M, Hormndendron, 750 X, growing tip seen with oil im- 

 mersion phase objective. N, O, yellow fever viral inclusion bodies, 700 X : A", bright- 

 field. 0, bright-contrast phase. (Councilman body at the left of center.) 



