684 The Outline of Science 



multiplied about three million times to give the total number of 

 red corpuscles in the body; a similar figure would be found for 

 other sorts of cells. 



The body is thus, in one sense, a huge cell-state, with a 

 cell-population thousands of times larger than the total human 

 population of the world. A single act of thought involves the 

 co-operation of a vast multitude of brain-cells; a single move- 

 ment of a limb implies the contraction of thousands of muscle- 

 cells, a single beat of the heart sends billions of blood-cells 

 whirling down the dark pipes that we call blood-vessels. Each 

 of these cells is a unit of life, comparable in some respects to a 

 single free-living cell, such as an Amoeba or a Slipper Animalcule. 

 The enforcement of harmony and co-operation among such a vast 

 multitude of units is the greatest achievement of evolving life. 

 How necessary such enforcement is, and yet how difficult, is 

 shown by the effects of cell-insubordination, as in cancer and 

 malignant growths. In cancer, a few cells embark upon a career 

 of unchecked growth and multiplication at the expense of the 

 rest, and by so doing involve themselves and the rest of the cell- 

 community in the common ruin of death. 



Reproduction 



One of the fundamental attributes of living matter per- 

 haps the most fundamental of all is its capacity for assimila- 

 tion, for building up into its own complex likeness the simpler 

 chemical compounds by which it is surrounded. What is more, 

 in all primitive forms of life, assimilation is more rapid than its 

 converse new living molecules are constructed and put into 

 place in the organism faster than the old ones are used up; the 

 result is growth. 



But to increase in size is to increase volume faster than sur- 

 face, and this is, metaphorically speaking, to increase your popu- 

 lation faster than you increase your import and export facilities. 



