Mast, Loeb's Mechanistic Conception of Life. 



very simple and plausible explanation; but Loeb himself found 

 that the reactions to light can be changed by certain alkalies, salts 

 and narcotics as well as by acids, and others have discovered that 

 the same changes can be produced by mechanical stimulation and 

 by changes in temperature. Why then select acid as the con- 

 trolling factor? Moreover he assumes that substances within the 

 body have the same effect as they do when outside, an assump- 

 tion which, as far as I am aware, has no foundation in facts. 



Of a similar nature is the argument (pp. ( J6 99) leading to 

 the conclusions that "Growth in animals is determined by the same 

 mechanical forces which determine growth in plants" and "Activity 

 plays the same role in the growth of a muscle that the temperature 

 plays in the growth of the seed." 



The consideration of only a portion of the known facts regard- 

 ing many phenomena has made it possible for Loeb to offer ex- 

 tremely simple and attractive explanations for them, explanations 

 which appear superficially plausible especialle to those not thoroly 

 grounded in the subject. 



Aside from those already referred to our author has made a 

 number of statements, direct or implied, which, altho of no great 

 consequence in the discussion, are of doubtful validity. For example, 

 (p. 41) "Experiments on the perception of light by our retina have 

 shown that the effect of light equals the product of the intensity 

 into the duration of illumination.'' (p. 43) Copepods have retinas, 

 (p. 50) More species react to light than to the electric current, 

 (p. 52) Animals are aggregates of independent hereditary qualities. 

 (p. 53) There is no indicatien of adaptation in the reactions of 

 animals to light. If they are positive at all they are positive to 

 all intensities above the threshold, (p. 54) Sudden decrease of in- 

 tensity of light causes a decrease in movements in planarians. 

 (p. 55) Hypotricha are sensitive to light, (p. 54) Haberlandt, 

 Nemec and F. Darwin do not attempt to explain plant tropisms 

 physico-chemically. (p. 196) "All as a rule or the majority of in- 

 dividuals of a species in a given region spawn on the same day." 

 (p. 174) "The egg membrane in Fundulus possesses a small opening, 

 the so-called micropyle, through which the spermatozoon enters 

 into the egg." (p. 74) "It can be shown that Infusoria, Coelen- 

 terates, and worms do not possess a trace of associative memory." 

 (p. 14) "The problem of the beginning and the end of individual 

 life is physico-chemically clear." 



After criticising former theories of fertilization as too vague to 

 be useful Loeb says (p. 115): "If we want to make new discoveries 

 in biology, we must start from definite facts and observations, and 

 not from vague speculations." I know 7 of no biologist who would 

 not whole-heartedly subscribe to this doctrine, but with all due 



