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SCIENCE 



[N. S. Vol. XLIV. No. 1140 



the idea of life. One can not define it in 

 terms of anything simpler, just as one can 

 not define mass or energy in terms of any- 

 thing simpler. But this one can say — that 

 each phenomenon of life, whether mani- 

 fested in "structure" or in "environment," 

 or in "activity," is a function of its rela- 

 tion to all the other phenomena, the rela- 

 tion being more immediate to some, and less 

 so to others. Life is a whole which deter- 

 mines its parts. They exist only as parts of 

 the whole. 



At first sight it might seem as if it must 

 be very difficult to make use of this concep- 

 tion as an instrument of research : for evi- 

 dently we can not investigate the parts 

 without investigating the whole. The diffi- 

 culty is only apparent. The whole is there, 

 however little we as yet comprehend it. 

 We can safely assume its presence and 

 proceed to discover its living details piece 

 by piece, in so doing adding to our knowl- 

 edge of the whole. If, on the other hand, 

 we attempt to take the organism to pieces, 

 or separate it from its environment, either 

 in thought or in deed, it simply disappears 

 from our mental vision. A living organ- 

 ism made up of matter and energy is like 

 matter and energy made up of pure time 

 and space : it conveys to us no meaning 

 which we can make use of in interpreting 

 the facts. 



But is there not matter and energy in a 

 living organism? Do we not assume this 

 at every step in physiology ? We make use 

 of the ideas of matter and energy in biol- 

 ogy, just as the physicist makes use of the 

 idea of extension in the investigation of 

 matter. To the biologist, however, the 

 structure and activity of an organism are 

 no mere physical structure and activity, 

 but manifestations of life, just as to the 

 physicist the extension of matter is no mere 

 mathematical extension, but a manifesta- 

 tion of the properties of matter, with a 

 physical and not a mere mathematical 



meaning. This is the answer to those who 

 point to the dependence of physiology on 

 physics and chemistry, and conclude from 

 this that physiology can not be anything 

 but a department of physics and chemistry. 

 By a similar chain of reasoning physics 

 would be nothing but a branch of mathe- 

 matics, and mathematics itself would melt 

 away into that universe of unconnected 

 "impressions" which David Hume imag- 

 ined, but Immanuel Kant showed to be non- 

 existent. 



The limits of time prevent my giving 

 further examples of the light which the 

 conception of the normal throws on the de- 

 tails of every part of physiology, and I 

 must now try to probe more deeply. It 

 may be pointed out that although it is use- 

 ful in matters of detail to bear in mind 

 that a living organism tends to maintain a 

 normal of both structure and activity, and 

 to pass through a normal life history, yet 

 in ultimate analysis all this must be due 

 simply to the reactions between its struc- 

 ture and physical and chemical environ- 

 ment. I will not at this point quarrel on 

 general grounds with the "must," but 

 simply endeavor to test it by the facts of 

 physiology. 



We can distinguish in a living organism 

 what seems a more or less definite struc- 

 ture of bony matter and connective tissue. 

 Yet we know that all this is built up, and 

 in adult life is constantly being pulled 

 down, rebuilt and repaired, through the 

 activities of living cells. It is thus within 

 the living cells that we must look for the 

 structure which is supposed to react so as 

 to maintain the normal. These cells are 

 made up of what has been called "proto- 

 plasm." Now the more we study proto- 

 plasm the more evident does it become that 

 this "substance" is extraordinarily sensi- 

 tive to the minutest changes in environ- 

 ment. Take away or diminish or increase 

 the minute traces of calcium or potassium 



