152 BOTANICAL GAZETTE [FEBRUARY 
say wherein the difference lay. After this all motion ceased and 
the protoplasm appeared coagulated. Under a high magnification 
(2200 diameters) the protoplasm was seen to be filled with small 
vacuoles which were so numerous that it had the appearance of 
a fine froth. These vacuoles were not visible before the organism 
was exposed to the light. 
The length of exposure necessary to bring about these changes 
varied from 30 to 100 seconds when the hydrogen discharge tube 
was Carrying 29 milliamperes. Since the effect on the organisms 
is additive, the entire exposure was not made at one time, but at 
intervals, so that the experiment often extended over an hour. 
Thus the changes produced by the light could be more carefully 
observed. 
Infusoria are very quickly cytolyzed by the rapid vibrations 
of these ultra-violet rays. The nature of the cytolysis varies 
greatly with the species, and, in some of the minor details, it varies 
with different individuals. 
The writer has observed three kinds of photo-cytolysis in 
ciliated infusoria: first, a cytolysis which is accompanied by the 
formation of vesicles on the surface; second, a cytolysis in which 
some of the internal portions of the protoplasm coagulate; and, 
third, a cytolysis in which some of the protoplasm disintegrates 
directly. The first two types of cytolysis were observed in Colpoda- 
like forms, and the third type was observed in Stylonychia. 
The cytolysis by vesicle formation requires an exposure of 
about 30 seconds when the discharge tube is carrying 18 milliam- 
peres. The vesicles are filled with a clear liquid and are often as 
large as the organism itself. Several vesicles may form and again 
disappear during the exposure. With sufficient exposure, the 
surface which separates the protoplasm from the fluid contained 
within the vesicle breaks, and the protoplasm flows out into the 
vesicle. A still longer exposure may cause the outer wall of the 
vesicle to rupture. The protoplasm then flows out into the sur- 
rounding water, with which it is miscible. 
In the cytolysis in which parts of the protoplasm coagulate, an 
exposure of a few seconds results in the formation of small masses 
of coagulum, which are at once extruded by the organism. Con- 
