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THE GENERAL CONDITIONS OF LIFE ••?11 



ho exteiuls the foncoptioii of life have had a metabolism. This 

 cannot be substantiated. It cannot be doubted, indeed, that these 

 masses possessed an extremely energetic internal motion ; and, 

 life is nothing but a complex motion, to which every other 

 molecular motion is allied in principle. Nevertheless, vital mo- 

 tion, metabolism, is a complex motion very sharply characterising 

 the living organism ; it consists in the continual self-decomposition 

 <if living substance, the giving-off to the outside of the decom- 

 position-products, and, in return, the taking-in from the outside of 

 certain substances, which give to the organism the material with 

 which to regenerate itself and grow by the formation of similar 

 groups of atoms, i.e., by polymerisation. This is characteristic of 

 all living substance. But that this peculiar complex motion 

 existed in the incandescent mixtures of the earth and has suffered 

 no interruption from that time down to the present living sub- 

 stance, is in a high degree doubtful. Mixtures of this kind, which, 

 as la\'a, can be observed at the present day in volcanoes, and there 

 are still at so high a temperature that in flowing from a cleft of the 

 crater over a precipice they present the wonderfully fascinating- 

 spectacle of an incandescent waterfall — these extremely liquid 

 mixtures, however mobile they may be, show no metabolism in the 

 real sense, and hence should not be termed living. Nor can the 

 original incandescent mass of the earth be so termed deliberately, 

 however impiressive and suggestive Prej'er's theory is. There then 

 remains as the sole difference between Preyer's doctrine and that 

 of spontaneous generation the point invohed in the "\ery unessen- 

 tial question, whether living substance has come from lifeless 

 substance gradually and by imperceptible transitions ; or whether 

 it has been formed more directly, as is the product of two bodies 

 in a chemical reaction in a test-tube, and has taken on its 

 characteristic properties. In neither case will the conclusion be 

 avoided that living substance once came from substances that are 

 customarily termed lifeless. 



2. The Descent of Lie in g SnJistanee 



Upion the basis of the ideas de\cioped by Ptltiger we ari' now in 

 a position to form in gross outline an approximate idea of the origin 

 of life upon the earth. The beginnings of living substance reach 

 down into the time when the earth's surface was still incandescent. 

 The compounds of cyanogen then present constitute the essential 

 material from which living substance took its origin. With their 

 propertv of ready decomposition they were forceil into correlation 

 with \arious kinds of compounds of carbon, whose origin was due 

 likewise to the great heat. When water was precipitated in the 

 form of liquid upon the earth's surface, these compounds entered 



