288 THE AMERICAN NATURALIST. (VoL. XXXIX. 
In order to prove this theory, Professor Smith showed by 
means of suspended indigo that when the diatom moves forward 
the particles of indigo gather around the central nodule of the 
valve and form a small mass which turns on itself just as if it 
was impelled by a jet of water proceeding from the valve at this 
point. Each of these little turbulent spheres after having 
acquired a certain size, falls apart and the particles which com- 
pose it are driven along the valves from front to back and accu- 
mulate behind the extremity of the frustule which, according to 
its progression, woüld be considered the rear. The particles 
move as if they were subjected to a current going from front to 
back, and reverse when the motion is reversed. That these cur- 
rents exist there can be no doubt, but that the motive power is 
not due to the expulsion of water will shortly be demonstrated. 
The first intimation of the true nature of this motion was 
suggested by the action of a lithia tablet in a glass of water. 
The bubbles of carbonicacid gas given off set up the exact 
. motions in the tablet that have been so often described for the 
movements of diatoms: * A sudden advance in a straight line, a 
little hesitation, then other rectilinear movements, and, after a 
short pause, a return upon nearly the same path by similar 
movements." 
Repeated experiments with compressed pellets evolving gas 
have shown that this is the usual motion produced by the evolu- 
tion of gas bubbles, and when pellets were made of the same 
shape as Navicula the movements of these diatoms were per- 
fectly duplicated. Boat-shaped pieces of aluminum two milli- 
meters thick were then made and on them were cut longitudinal 
grooves to resemble those of the diatom. When placed in 
strong caustic soda solution the movements of the metal pro- 
duced by the evolution of hydrogen gas again duplicated those 
of the diatom ina remarkable manner. The metal having the 
grooves had a greater power of motion than that without th 
grooves. 
If we consider that the diatom contains chlorophyll bands which 
"a exposed to a strong light rapidly evolve oxygen, and if we 
take into account the fact that the motion does not take place 
unless the light is fairly strong, we have then a conception of | 
the true nature of the movements of these organisms. 
