REACTION IN AMOEBA TO LIGHT 
275 
of the experiment, one could hardly bear to look through the micro- 
scope when the yellow was reflected, while in the case of blue, 
the region of maximum stimulation for iVmoeba, there was no 
unpleasant stimulation whatever to the eye. 
Furthermore, it cannot be said without qualification that the 
actinic rays are most efficient in stimulating Amoeba, for in most 
photochemical reactions the violet and ultra violet are most 
active. As a matter of fact, however, the current idea that only 
the shorter waves of the spectrum are actinic is not supported by 
the results of recent experiments of Stobbe (1908) and others on 
photochemical reactions. Nor can it be said that the region of 
greatest efficiency in the solar spectrum is the same for all of the 
lower organisms, plants as well as animals, as maintained by 
Loeb (1905, p. 194) and Davenport (1897, p. 202), for Strasburger 
(1878) found the region of maximum stimulation for swarm spores 
in the violet; Wiesner (1879) found that for higher plants at the 
lower limit of the violet; Bert (1869), Lubbock (1882) and others 
found that for Daphnia and related forms in the green or yellow; 
Engelmann (1883) found that for Bacterium photometricum in 
the infra red, and Verworn (1899) maintained that all regions of 
the spectrum are equally active in stimulating Oscillaria. 
All reactions to light are probably caused by or at least associa- 
ted with chemical changes induced by the illumination. But the 
fact that different organisms are not equally stimulated by the dif- 
ferent colors of the spectrum indicates that the chemical changes 
associated with the reactions are not the same in all organisms. 
This point is however, not irrevocably established, for while it 
is generally true that the reacting substances are different when- 
ever photochemical reactions are caused by different colors, it 
is well known that the color which causes reactions between dif- 
ferent compounds may be changed by the addition of certain 
substances which do not take part in the reactions. Thus it may 
be that the cause of difference in the response to different colors 
in organisms is not due to different photochemical substances 
within the organism, but to the presence of substances which do 
not take part in the reactions. 
