112 DYNAMICS OF LIVING MATTER 



There are, however, a number of biological effects of temperature 

 for which we cannot yet indicate the physical or chemical variable. It 

 is generally known that in many hibernating northern chrysaUds the 

 velocity of metamorphosis is increased if the chrysalids are exposed 

 for some time to a temperature of o°. This fact is possibly related 

 to the experience, that treatment with ether can hasten the develop- 

 ment of buds and plants. An equally puzzHng effect of heat is the 

 influence a low temperature has upon the production of wings in Aphides. 

 As long as the temperature is high and the moisture sufficient, plant 

 lice are wingless; but if the temperature be lowered, wings begin to 

 grow. In this case the lowering of temperature favors the growing of 

 an organ, an effect which is rather paradoxical in view of the fact that 

 the phenomena of development seem to be plainly a function of the 

 reaction velocity of underlying chemical processes. 



The late Dr. Greeley * showed that a certain group of Infusorians, 

 M'onas, can at any time be caused to form spores by exposing them for 

 a short time to a low and afterward to a higher temperature. Forms 

 of irritability can also be varied through the influence of temperature. 

 I have shown that positively heliotropic Copepods can be made nega- 

 tively heliotropic by raising the temperature, and negatively heUo- 

 tropic Copepods can be made positively heliotropic by lowering the 

 temperature. This will be more fully discussed in the next lecture. 

 In passing I may mention that certain changes — seasonal variations — 

 can be brought about by changes in temperature.f 



2. General Effects of Radiant Energy upon Living Matter 



The electromagnetic theory of light has led to the idea that there 

 must exist besides the already known ether waves other waves on both 

 sides of the scale. Hertz discovered the method by which we can 

 experiment with ether waves of several centimeters or more with the 

 same certainty as was before possible with the shorter waves, which 

 are able to produce sensations of heat or light. The question had to 

 be put whether or not Hertzian waves had any physiological effect. 

 I made eight years ago an extended series of investigations on this sub- 

 ject, and the first experiments seemed to speak in favor of the idea that 

 the Hertzian waves have effects upon the nerves; but I was able to 

 show by a closer analysis that these apparent effects of these waves 

 were not due to the oscillatory character of the discharge, and that 

 the same results could be brought about by nonoscillatory discharges. J 



* A. W. Greeley, Biological Bulletin, Vol. 3, p. 165, 1902. 



t Wolfgang Ostwald, Zeitsch.fUr Entwickelungsmechanik, Vol. 18, p. 415, 1904. 



X Loeb, Pfliiger's Arckiv, Vol. 67, p. 483, 1897 ; and Vol. 69, p. 99, 1897. 



