30 The Mechanistic Conception of Life 



animal is small, according to the law of Bunsen, it must take a 

 comparatively long time until the animal is automatically 

 oriented by the light, since according to this law the photo- 

 chemical effect is equal to the product of the intensity of the 

 light into the duration of illumination. If, however, the inten- 

 sity of the light is strong or the active mass of the photochemical 

 substance great, it will require only a very short time until the 

 difference in the mass of photochemical reaction products on 

 both sides of the animal reaches the value which is necessary 

 for the automatic turning to (or from) the light. The behavior 

 of the animals agrees with this assumption. If the light is 

 sufficiently strong the animals go in an almost straight line to 

 the source of light; if the intensity of light (or the mass of 

 photosensitive substances on the surface of the animal) is 

 small the animals go in irregular lines, but at last they also 

 land at the source of light, since the directing force is not 

 entirely abolished. It will, however, be necessary to ascertain 

 by direct measurements to what extent these phenomena in 

 animals are the expression of Bunsen-Roscoe's law. But we may 

 already safely state that the apparent will or instinct of these 

 animals resolves itself into a modification of the action of 

 the muscles through the influence of light; and for the meta- 

 physical term ''will" we may in these instances safely substi- 

 tute the chemical term ''photochemical action of light." 



Our wishes and hopes, disappointments and sufferings have 

 their source in instincts which are comparable to the light 

 instinct of the heliotropic animals. The need of and the 

 struggle for food, the sexual instinct with its poetry and its 

 chain of consequences, the maternal instincts with the felicity 

 and the suffering caused by them, the instinct of workmanship, 

 and some other instincts are the roots from which our inner life 

 develops. For some of these instincts the chemical basis is at 

 least sufficiently indicated to arouse the hope that their analysis, 

 from the mechanistic point of view, is only a question of time. 



