INTRODUCTORY 19 



the property in some plants or animals which compels 

 them to go towards the light. I have examined this sub- 

 ject and I am certain that no such property or thing ex- 

 ists ; that this high sounding word describes something 

 that exists only in the imagination of some person. How- 

 ever, the books are full of it and Jacques Loeb. M. D. PH. 

 D and S. C. D. (member of the Rockefeller Institute) in 

 his book on the Physico-Chemical or Mechanistic theory 

 of life tries to show that this fact is the most significant 

 proof that life is merely a chemical force. Here is what 

 he has to say on the subject : "The positively heliotropic 

 animals which go instinctively to a source of light have 

 in their eyes photo sensitive substances, which undergo 

 chemical alterations by light. The products formed in 

 this process influence the contraction of the muscles 

 mostly indirectly through the nervous system. In a series 

 of experiments I have shown that the heliotropical reac- 

 tions of animals are identical with the heliotropical actions 

 of plants. In plants only the more refrangible rays from 

 green to blue have these heliotropical effects, while the 

 red and yellow rays are little or less effective, and the 

 same is true for the heliotropical reaction of animals." 



Now here follow some of his experiments in the follow- 

 ing words : "Some experiments on winged plant lice may 

 serve as an introduction, etc. * * * In order to obtain 

 the material, potted rose bushes infected with plant lice 

 are brought into a room and placed in front of a closed 

 window. If the plants are allowed to dry out, the aphides 

 (plant lice), previously wingless, change into winged in- 

 sects. After this metamorphosis the animals leave the 

 plants, fly to the window and there creep upward on the 

 glass." Then he makes the further remark : "It can be 

 demonstrated in these animals that the direction of their 

 progressive movements is just as unequivocally gov- 



