THE WONDERS OF LIFE 



a mechanical structure. In these primitive "organisms 

 without organs" (chromacea and bacteria) the sole cause 

 of life is the invisible chemical structure of the plasm 

 and the metabolism effected by this. As soon as this 

 ceases death takes place {cf. chapter ix.). In the case of 

 all other organisms the comparison is useful in so far as 

 the orderly co-operation of the various organs or parts 

 accomplishes a certain task by the conversion of virtual 

 into active force. But the great difference between the 

 two is that in the case of the machine the regularity is 

 due to the purposive and consciously acting will of man, 

 whereas in the case of the organism it is produced by 

 unconscious natural selection without any design. On 

 the other hand, the two have another important feature 

 in common in the limited span of life which is involved 

 in their being used up. A locomotive, ship, telegraph, 

 or piano, will last only a certain number of years. All 

 their parts are worn out by long use, and, in spite of all 

 repairing, become at last useless. So in the case of all 

 organisms, the various parts are sooner or later worn 

 out and rendered useless; this is equally true of the 

 organella of the protist and the organs of the histon. 

 It is true that the parts may be repaired or regenerated; 

 but sooner or later they cease to be of service, and 

 become the cause of death. 



When we take the idea of regeneration, or the re- 

 cuperation of parts that have been rendered useless, 

 in the widest sense, we find it to be a universal vital 

 function of the greatest importance. The whole metab- 

 olism of the living organism consists in the assimilation 

 of plasm, or the replacing of the plasma-particles which 

 are constantly used up by dissimilation {cf. chapter x.). 

 Verworn has given the name of hiogens to the hypo- 

 thetical molecules of living matter — which I regard with 

 Hering as endowed with memory, and (1875) have called 

 plastidules. He says: "The biogens are the real 



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