BOOK XIII 

 REPRODUCTION 



CHAPTER LXXVII 

 GROWTH AND REPRODUCTION 



LIVING matter is characterized by the fact that ft can grow, and 

 by the fact that it can only be produced by the action of living matter ; 

 that nothing but living matter can organize the materials and forms 

 of energy of the noa-living into the living world; that each living 

 cell possesses a type of energy which is, so to speak, attuned to the 

 retention of certain attributes of structure and function, and to the 

 capacity of communicating these onward to its offspring a capacity 

 which is termed heredity; that each living organism dies after a 

 certain period of existence. A unicellular organism placed in a drop 

 of water divides and divides into a multitude, but after a time the 

 generations usually begin to deteriorate, become feebler, and finally 

 die out. If, however, one of the shoal be placed in a vessel with one 

 of another stock of the same species, the two will fuse and become 

 one, with vigour entirely restored. 



It has been stated that a single-celled paramoecium by successive 

 division, first of itself and then of its progeny over a period of five 

 years, possesses the power to reproduce to the 3,029th power, or a 

 volume of protoplasm equal to 10 1000 times the volume of the earth. 



The higher animals are vast colonies of cells. Most of these 

 eventually become feeble, and die in due season; but the generative 

 cells fuse, reinvigorate each other, and continue the race. Thus 

 does a man live again in his children. 



The growth of the tissues depends upon the power of their cells 

 to multiply. The tissues interact upon one another, so as to restrain 

 and confine the growth of any one tissue within its proper boundary. 

 How this restraint is brought about we do not know. Loss of this 

 restraint, or the overpowering energy of growth of any one tissue 

 results in the formation of tumours, benign or cancerous. 



It has recently been shown that the growth of human tissues 

 constitutes a type of its own, differing markedly from the growth in 

 other mammals, such as the cow, horse, sheep, pig, and other domestic 

 animals. From calculations made upon the animals during the 



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