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SCIENCE 



[N. S. Vol. XXIX. No. 751 



acteristic phenomenon of living matter, in- 

 volves intramolecular change ; consequently 

 the molecule, and not the cell, is the unit of 

 life. Matter is endowed with life when it 

 becomes the seat of that form of energy 

 which makes of it a metabolic mechanism. 

 As soon as a molecule becomes the seat of 

 assimilation and excretion it is no longer 

 dead ; it lives. As a result of assimilation, 

 it acquires the property of building up its 

 own substance ; then polymerization follows 

 and reproduction in its simplest form be- 

 gins. The one phenomenon always mani- 

 fested by living matter and never exhibited 

 by non-living matter is metabolism. Ver- 

 worn says : 



Vital motion, metabolism, is a complex motion 

 very strongly characterizing the living organism; 

 it consists in the continued self-decomposition of 

 living substance, the giving off to the outside of 

 the decomposition products, and in return, the 

 taking on from the outside of certain substances 

 which give to the organism the material with 

 which to regenerate itself and grow by the forma- 

 tion of similar groups of atoms, i. e., by polym- 

 erization. This is characteristic of all living 

 substance. 



Aristotle apparently recognized that 

 metabolism is the one characteristic of 

 living matter, for he said : 



Life is the assemblage of the operations of 

 nutrition, growth and destruction. 



The Greek philosopher and scientist did 

 not know all that is now known about cells, 

 molecules, atoms and electrons, but we 

 must admit that he had a fairly clear con- 

 ception of the most essential characteristic 

 of living matter. 



Du Bois Raymond said that the matter 

 in crystals and non-living substances is in 

 a condition of indifferent static equilibrium, 

 while that in living bodies manifests a 

 motile equilibrium. Bechterew says that 

 we know of nothing in the inorganic world 

 that contains or consists of motile com- 

 pounds. 



Matter is alive when it feeds and excretes. 



Crystals grow, and in a sense they multiply, 

 but their growth is not intramolecular; it 

 is by accretion. The living molecule not 

 only absorbs; it assimilates. It chemically 

 alters what it receives. The atomic groups 

 taken into living molecules enter into new 

 combination. The living molecule is not 

 stable ; it is highly labile. Its composition 

 is never constant ; it is never in a condition 

 of equilibrium. There is a constant reac- 

 tion between the living molecule and other 

 molecules. This reaction consists in the 

 absorption and assimilation of certain 

 atomic groups and the easting out of others. 

 Apart from other matter it could not exist. 



What is accomplished by this constant 

 interchange of atomic groups between the 

 living molecule and outside matter ? It is 

 for the purpose of supplying the living 

 molecule with energy. Allen expresses 

 this fact as follows : 



The most prominent and perhaps most funda- 

 mental phenomenon of life is what may be de- 

 scribed as the energy traffic, or the function of 

 trading in energy. The chief physical function of 

 living matter seems to consist in absorbing energy, 

 storing it in a higher potential state, and after- 

 wards partially expending it in the kinetic or 

 active form. We find in living matter a peculiar 

 proneness to change its composition under the 

 stimulus of slight changes in the energy-equilib- 

 rium between itself and its surroundings, energy 

 being readily absorbed and readily dispersed. The 

 absorption of energy coincides with deoxidation 

 and the building up of large molecules. The 

 building up of these large molecules is always 

 accomplished by slow steps; but when formed, the 

 said molecules are very unstable, irritable or, in 

 modern phrase, labile. They may be broken down 

 by degrees in some instances; in others their 

 structure may be so precarious as to collapse on 

 the slightest disturbance. 



The lability of such a molecule may be com- 

 pared to that of a house of cards, which can be 

 taken to pieces card by card, or may collapse at 

 once. But the word lability is applied not only to 

 destructive, but also to constructive instability. 

 The molecules of living substance are prone to 

 constructive as well as destructive changes; but 

 as in the house of cards the constructive changes 



