Metabolism 17 



combined with the protoplasm, but is retained 

 mechanically within it. The function of chloro- 

 phyll is to absorb certain rays of light, and 

 enable the protoplasm with which it is inti- 

 mately connected to avail itself of radiant 

 energy of the sun's rays, for the construction of 

 organic substance from carbon dioxide and 

 water. 



Every kind of healthy living matter pos- 

 sesses the power of helping to convert the 

 nutrient matter which, as a rule, is carried to it 

 by the circulating fluid into such a form as 

 can be incorporated with its protoplasmic ele- 

 ments, thus replacing its worn-out particles; 

 this process is technically known as Meta- 

 bolism. Professor Huxley, when referring to 

 this power, describes the incoming atoms as 

 being piled up in the cell under the action of 

 chemical force, while before they leave it they 

 tumble down into smaller heaps. The energy 

 set free in the tumbling down of these atom 

 groups affords a constant store of working 

 energy to the cell-contents. 



The human brain, for our purposes, may be 

 described as consisting of an innumerable multi- 



B 



