THE BIOLOGY OF DAILY LIFE. 33 



us begin by taking a summary view of the whole 

 process, by which animal life is carried on, under 

 normal conditions. 



Let us take Herbert Spencer's own words, and 

 follow his comprehensive and masterly presentment 

 of the facts as attentively as we can. Then return to 

 this subject with clear ideas. 



" In the two fundamental functions of nutri- 

 tion and respiration we have the means by 

 which the supply of materials for this active 

 molecular re- arrangement [which organisms, 

 and especially animal organisms, display] is 

 maintained. 



" The process of animal nutrition consists in 

 the absorption partly of those complex sub- 

 stances, which are thus highly capable of being 

 chemically altered, and partly in the absorption 

 of simpler substances capable of chemically 

 altering them. . . . 



" The inorganic substance, however, on 

 which mainly depend these metamorphoses in 

 organic matter is not swallowed along with the 

 solid and liquid food, but is absorbed from the 

 surrounding medium air or water, as the case 

 may be. Whether the oxygen taken in either 

 as by the lowest animals, through the general 

 surface, or, as by the higher animals, through 

 respiratory organs, is the immediate cause of 

 those molecular changes that are ever going on 

 throughout the living tissues ; or whether the 

 oxygen playing the part of scavenger merely 

 aids these changes by carrying away the pro- 

 ducts of decompositions otherwise caused; it 



D 



