THE NATURAL HISTORY OF TUMOURS 557 



growth is inherent in all living things, so long as they are 

 living. It is born in them with their birth, lives with them 

 throughout their lives, and dies with them when they die. 

 So long as conditions are favourable, it knows no bounds or 

 limits. Reproduction is growth beyond the individual. 



This is not difficult to understand in the case of primitive 

 organisms such as those which existed in that immeasurably 

 remote period when life made its appearance upon earth. 

 Their structure was of the simplest, and their growth continued 

 until at last their size became so great that they were com- 

 pelled to divide. The dimensions reached before division 

 took place probably varied in each case. There was no definite 

 limit. It depended entirely upon circumstances. But when 

 circumstances continued to be the same for generation after 

 generation, the intervals gradually became more and more 

 regular, and a certain uniformity was introduced. The power 

 of reproducing itself directly as soon as a certain size was 

 reached belonged to every organism as part of its birthright. 

 It is part of the birthright still. 



The Division of the Organism into Germ Cells and 



Somatic Cells 



A change took place when the metazoa came into exist- 

 ence. Increase in size in a multicellular organism necessarily 

 involves division of labour. The function of reproduction, 

 for example, can no longer be carried on equally well by all 

 parts of the organism indiscriminately. One part better 

 suited by locality or arrangement is marked off from the rest 

 and undertakes the work of maintaining the race. The cells 

 of which it is composed give up everything else. They do 

 nothing for themselves. The rest of the cells, on the other 

 hand, the somatic ones, lose all concern with reproduction 

 and devote themselves entirely to the work of every-day life 

 and the maintenance of the individual. This is the primary 

 division. On this is based the classification of the tissues 

 and of the tumours that grow from them. 



At the first the distinction between the two sections is 

 not well marked. For a long time the cells of one group can 

 take the place of those of the other and perform all their 

 duties if required. In the ova of some of the echinodermata, 



