September 17, 1915] 



SCIENCE 



379 



which is the very basis of the mechanistic 

 physiology, is " a gigantic leap in the dark." 

 To be sure, the difficulty of making out this 

 causal connection might be due solely to the 

 complexity of the cell, nevertheless " the point 

 must be emphasized that in the case of stim- 

 ulus and response there is in reality no experi- 

 mental evidence whatsoever that the process 

 can be understood as one of physical and 

 chemical causation." No real quantitative 

 relation between the supposed cause and the 

 effect can be traced. 



No doubt such information as we now pos- 

 sess will continue to increase, biophysics and 

 biochemistry to unfold, but there is no reason 

 to suppose that this kind of information will 

 in the future serve as an explanation of that 

 which in the past it has totally failed to 

 explain. 



Historically, in spite of the great services of 

 physics and chemistry to biology, " the mech- 

 anistic theory has, oil the whole, fared very 

 badly." Cell-growth and cell-nutrition, absorp- 

 tion and secretion, have not been mechan- 

 istically explained. Mechanistic theories of 

 respiration and metabolism, of muscular 

 movement and other physiological movements, 

 have also failed. And as the science develops 

 we seem to get further and further away from 

 any prospect of success in siich enterprises. 

 In truth ignorance alone could have justified 

 the earlier crude mechanistic theories of the 

 intracellular processes. For " what the mech- 

 anistic theory must assume in the case of an 

 organism such as man is a vast assemblage of 

 the most intricate and delicately adjusted cell- 

 mechanisms, each mechanism being so con- 

 stituted as to keep itself in working order year 

 after year, and in exact coordination with the 

 working of the millions of other cell-mechan- 

 isms which make up the whole organism." 



But the facts of reproduction and heredity 

 involve still greater difficulties, for we have 

 reason to believe that the whole adult mechan- 

 ism has come from the nuclear material of the 

 fertilized germ cell. " On the mechanistic 

 theory this niicleus must carry within its sub- 

 stance a mechanism which by reaction with the 

 environment not only produces the millions of 



complex and delicately balanced mechanisms 

 which constitute the adult organism, but pro- 

 vides for their orderly arrangement into tissues 

 and organs, and for their orderly development 

 in a certain perfectly specific manner." And 

 yet, according to the mechanistic view, this 

 structure of inconceivable complexity is capa- 

 ble of dividing itself to an indefinite extent 

 while retaining its original structure. " The 

 real difficulty for the mechanistic theory is 

 that we are forced, on the one hand, to postu- 

 late that the germ-plasm is a mechanism of 

 enormous complexity and definiteness, and, on 

 the other, that this mechanism, in spite of its 

 absolute definiteness and complexity, can divide 

 and combine with other similar mechanisms, 

 and can do so to an absolutely indefinite ex- 

 tent without alteration of its structure. On 

 the one hand we have to postulate absolute 

 definiteness of structure, and on the other 

 absolute indefiniteness." 



Hence, says Haldane, the mechanistic theory 

 of heredity is impossible. 



The mechanistic theory of heredity must in- 

 volve in its downfall every other part of biol- 

 ogy. " If we can not frame a mechanistic 

 theory of heredity we are equally at a loss in 

 connection with the ordinary phenomena of 

 metabolism, and we have no right to use 

 mechanistic hypotheses in connection with 

 these phenomena." And finally Haldane con- 

 cludes : " The phenomena of life are of such a 

 nature that no physical or chemical explana- 

 tion of them is remotely conceivable." 



This conclusion leads to the second half of 

 the book which begins with a philosophical 

 discussion of the nature of reality. Out of 

 this is developed the Hegelian conclusion " that 

 a special category or categories ought to be 

 added (to those of the physical sciences) for 

 organic life, as the idea of life is one of the 

 fundamental ideas. There is no reason why 

 a category or general conception of life should 

 not be just as much constitutive of our experi- 

 ence as the category of substance. Here, there- 

 fore, we have a possible way out of our difS.- 

 culties with the mechanistic theory of life. In 

 trying to reduce life to physical and chemical 

 mechanism we are perhaps in some way con- 



