fiSii Mast, Locb's Mechanistic Conception of Life. 



underlying the theory of natural selection which was definitely 

 rejected in another section. But his whole argument in support 

 of his contention rests on highly speculative premises, that is, that 

 hybrids occur extensively under natural conditions and that only 

 relatively very few organisms produced thus can live. Moreover, 

 this hypothysis has no bearing on organisms which reproduce only 

 asexually. 



His final conclusion regarding the reduction of form production 

 and adaptation to "blind forces" hinges on the meaning implied by 

 the expression "blind forces"; and in the absence of a definition 

 of this extremely vague term, it would be folly either to agree or 

 to disagree with the conclusion. It may be said however that if 

 the author intends to maintain that we have any real insight into 

 the reason why certain chemical elements are durable and others 

 are not (quoted above), further than the fact that this has been 

 observed to be so he will be supported by few if any of those com- 

 petent to judge in the matter. 



The treatment of the problem of behavior occupies nearly one- 

 fourth of the entire volume. Loeb holds that the elements of all 

 behavior both in plants and in animals, including all psychic 

 phenomena, are tropisms. These, he maintains, have been mechanic- 

 ally explained and since the elements have been reduced to 

 mechanical principles all of the compounds constructed from them 

 can be similarly reduced. 



A tropism is, according to Loeb, a process of orientation due 

 to the continuous action of the stimulating agent on symmetrically 

 situated sensitive tissues. He says (p. 219): "In . . . heliotropic an- 

 imals in which the symmetrical muscles participate equally in 

 locomotion, the symmetrical muscles work with equal energy as 

 long as the photochemical processes in both eyes are identical. 

 If, however, one eye is struck by stronger light than the other, 

 the symmetrical muscles will work unequally." In another con- 

 nection (Dynamics of living Matter, p. 135) he says specifically that 

 tropisms are "a function of the constant intensity". Reactions in 

 accord with these ideas would, of course, result in orientation. The 

 question is arc the observed orienting reactions actually of this 

 nature; are they controlled by the continuous action of the stimulat- 

 ing agent? One or both of these questions have been conclusively 

 answered in the negative for the following organisms: Eui/Inta, 

 tifattor and all of the other unicellular organisms, with the possible 

 exception of An/flxi, in which the process of orientation has been 

 studied, Volro.n- and all other colonial forms tested, Hydra, fire- 

 Hies, fiddler-crabs and toads. (See Mast, "Light and the Behavior 

 of Organisms".) In most of these forms it has been shown that 

 orientation is dependent upon the time rate of change in the inten- 



