ij I.IIK : OIILINKS OF GENERAL BIOLOGY 



(atty acids diid aimnonia. To include the two sets of processes, 

 anabolism ;u)d katalx>lisni. the general term metabolism is used. 

 It is convenient to use this term in a broad way, as the equivalent 

 of the (uTnian word ">toflwechsel" (change of stuff), to include 

 all the chemical routine of the living body. The present point is 

 that living alwa\-s involves the metabolism of proteins; and that 

 this is s<) regulated that the living creature lives on from day to 

 day. or from year to year, even from century to century. 



There is intense activity of a simple kind when the fragment 

 of |v>tassium rushes al)out on the surface of the basin of water, 

 but it differs markedly from the activity of the Whirligig Beetle 

 (Gynnu>) that swims swiftly to and fro, up and do\NTi in the pool. 

 The difference is not merely that the chemical reactions in the 

 beetle are much more intricate than is the case with the potassium, 

 and that they involve eventually the down-breaking and up- 

 building of j>rotein molecules. The big difference is that the potassium 

 fragment soon flares all its activity away and changes into some- 

 thing els<'. whereas the beetle retains its integrity and lasts. It may 

 l)e s«iid, indeed, that it is only a difference in time, for the beetle 

 eventually dies. But this is to miss the point. The peculiarity we 

 are emphasising is that for certain variable periods the processes 

 of winding-up in organisms more than comjx'nsate for the processes 

 of running down. A primitive living creature was not worthy of the 

 name until it could balance its accounts for some little time, until 

 it could in some measure counter its katabolism by its anabolism. 

 iNrhaps it was only a creature of a day, which died in the chill of 

 its first night, probably after reproducing its khid; but the point 

 is that during its short life it was not like a glorified potassium 

 fragment or a clock running down. It was to some extent winding 

 its«lf up as well as letting itself run down. It was making ends 

 mtrt physiolcigically. 



In the immens<> furnaces of the stars, with unthinkably high 

 trm|vratur<s. it may Ix- that hydrogen is being lifted up into more 

 complex forms of matter, but on the earth all the chemico-physical 

 cltK-ks are running down. I'ranium, by a partial disintegration of 

 its atomic nurlrus, may give rise to ionium, which may give rise 

 to radium, which by giving off lu Hum may give rise to lead. Or 

 uranitun may givi- rise tf) ]>rotactinium, which produces actinium, 

 which prcKlufcs had. Other instances are well known. But while 

 had Mcnvs to W readily bom and does not die, there does not 

 seem to U- at prevnt on the earth any process working the other 

 way and prcwluc ing heavy atoms like those of uranium. In the 

 littlr corner of the \uiivers<' where we move, we are living in a time 

 of thr running down of chemico-physical clocks. But the charac- 

 teristic of living organisms is that they wind themselves up. 



In an essay entitled The Abundance of Life, published many 



