CHAPTER XV 



THE PHYSICAL BASIS OF LIFE 



Whenever we find matter which assimilates and 

 multiplies, we find it consists of a substance with 

 a certain more or less definite chemical constitu- 

 tion, and this physical basis which shows the so- 

 called vital functions is called protoplasm. Cows 

 and cabbages, microbes and men, midges and 

 mammoths are all made of this substance, and 

 they all are able to multiply, and all are able to 

 assimilate their food, or to weave the food atoms 

 into this same substance. The atoms that make 

 the machinery of life are only four — carbon, 

 hydrogen, oxygen, and nitrogen. Usually in 

 association with these we find also sulphur, 

 phosphorus, iron, calcium, sodium, and a few 

 other elements, but only the quartet carbon, 

 hydrogen, oxygen, and nitrogen are necessary to 

 make the compound which is able to unweave 

 itself, as Penelope unwove her web, and then to 

 build itself up again just the same from the atoms 



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