ON THE VITALLSTIC VIEW uF NATCRE. 445 



expression of anatomical observations and theories repre- 

 senting an enormous amount of research, labour, and in- 

 genuity, but they iuvohc no new line of reasoning, and 

 they belong, accordingly, more to the history of Science 

 than to that of Tliought. 



The first to attempt a mechanical explanation of the . *■'-., 

 process of cellular division was Mr Herbert Spencer,^ LTgrovrth.'^ 

 who, in his 'Principles of Biology' (I860), pointed out 

 that there exists a limit of growth through assimilation 

 or intussusception, inasmuch as volume and mass increase 

 at a greater rate than the surrounding surface through 

 which communication with the environment is afforded. 

 A resultant tension brings about an increase of surface 

 through rupture, and restores the balance between the 

 contained mass and the surface. In his analysis of this 

 process of readjustment, Spencer has given mechanical 



^ The principle here referred to 

 s-ometimes goes under the name of 

 the Leuckart-Spencer principle, it 

 having heen suggested independ- 

 ently by Rudolf Leuckart, Herbert 

 Spencer, and Alexander James. It 

 requiret), of course, a great many 

 qualifii'ations. See the ' Principles 

 of IJiology,' vol. i. part 2, chap. i. 

 But " it follows from these con- 

 siderations tliat the cell can never 

 surpass a certain size ; for if the 

 disturbance of metaVjolism that 

 arises because of the increasing 

 disproportion between the more 

 superficial and the deeper layers 

 has reached a certain extent, the 

 cell can no longer continue living 

 in its existing form. Thus the 

 remarkable fact is exiilained very 

 simply, tliat no cells of constant 

 form are known that are larger 

 than a few millimetres in diameter, 

 and thus we are made to under- 

 stand why the development of 



large 



organisms is only possible 

 by the arrangement of the living 

 substance into an aggregate of 

 small cells instead of into a single 

 cell, for example, of the size of a 

 man. ... If, therefore, the living 

 substance of such a cell is not to 

 perish by growth, at some period in 

 its growth a correction of this dis- 

 proportion between mass and sur- 

 face and of the disturbance of 

 metabolism conditioned by it must 

 come in : such a correction is realised 

 in the reproduction of the cell by 

 division. The repnjduction of the 

 cell by division is accordingly to be 

 considered merely as a lesult of 

 growth, and the morphologists for 

 a long time have rightly termed 

 i-epniduction a continuation of 

 growtli, ' a growth beyond the 

 measure of the individual ' " (Ver- 

 worn, ' General I'hysiology,' Engl, 

 transl., p. 530, &c.) 



