328 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1937 



(fig. 2-B). The thickness of the layer is then regulated by inhaling 

 the excess of the liquid until the cells are lightly compressed between 

 the cover slip and the surface of the oil (fig. 2-C). Certain motile 

 organisms, such as rotifers, larvae, or ciliated Infusoria can thus be 

 rendered immovable. In the same manner, excess of oil can be 

 removed. The aqueous liquid, thanks to its adherence to the glass, 

 forms a tliin layer under the oil. 



Owing to all these improvements, Dr. Comandon has made wonder- 

 ful moving pictures with the microscope. Our readers can readily 

 appreciate this by examining the few views reproduced here, although 

 they are inanimate on the pages of our article. The films on the 

 black background are made by using the ultramicroscope lighted by an 

 electric arc. 



REPRODUCTION OF AMOEBAE 



When numerous unicellular organisms find themselves in unfavor- 

 able conditions, they undergo a change of form. Certain bacteria 

 become deformed and go into involution; certam protozoa encyst. 

 When the medium returns to a favorable state, they come out of the 

 cysts and resume their customary shapes. Plate 3, figure 1, represents 

 five amoebae which have been encysted for several weeks. Their 

 protoplasm is in a state of complete repose. At their right can be 

 seen a wandering amoeba. The diameter of these cysts is from 

 0.013 to 0.01 G millimeter. 



Figure 2, which foUows, taken at 4 o'clock, shows a cyst on the point 

 of breaking. The projection shows the very lifelike movements of the 

 protoplasm of the amoeba in its cyst and a contractile vacuole has 

 appeared. At 4:36, the amoeba tears open the cyst toward the right 

 (fig. 3), and at 5:32 the young amoeba escapes through this narrow 

 opening (fig. 4). 



Figure 5 shows a young amoeba which is beginning to take nourish- 

 ment; it has already collected several bacteria with the posterior part 

 of its body. Finally, figure 6 represents the most usual mode of 

 reproduction of the amoebae — simple division. 



DIVISION OF TRYPANOSOMES 



The trypanosomes, among which are found species pathogenic to 

 man, such as Trypanosoma gambiense, which is the agent of sleeping 

 sickness, are Protozoa. They generally multiply by longitudinal 

 division as shown in plate 4, where trypanosomes are shown undu- 

 lating among the spherical red blood corpuscles m the blood. 



THE LIFE OF AMOEBAE 



Plate 5, figure 1, shows an amoeba taking nourishment which con- 

 sists of an alga. It is 19 minutes 50 seconds past 1 1 o'clock; a pseudo- 



