sponsibility of caring for them, and every one who has cared for 

 domestic animals, knows what constant attention must be given to keep 

 them suppHed with food, water, sheher, and other "necessities of hfe." 

 And who can overlook the fact that it requires attention to maintain 

 his own physical health? In the laboratory this dependence upon the 

 environment is readily tested experimentally by any method of isola- 

 tion which will prevent an animal from securing any "vital necessity" : 

 as air — when sealed in a vessel ; or food — when locked up without it ; 

 or a favorable temperature. No animal can survive such isolation 

 from its normal environment. Every student of animals in nature 

 must also realize that similar supplies and conditions determine and 

 control the existence and welfare of all zuild animals. The animal is 

 not self-sustaining, but requires a constant intake of energy and sub- 

 stance from its environment. Chemical methods will readily show the 

 source from which the materials composing the animal body have been 

 derived. The ash came from the soil or rock, and shows the animal's 

 dependence upon the solid earth; the liquids came from the water ot 

 the earth and constitute from fifty to ninety-five per cent, of the bulk 

 of the animal's body, showing that a relatively large quantity of this 

 substance is essential to all living animals ; the abundant gaseous ele- 

 ment was derived from the atmosphere, to which it will again return. 

 The substance composing the animal body is thus derived mainly from 

 the water and the air rather than from the relatively inert and stable 

 earth. It will be profitable for us to imagine these proportions so 

 changed that the solids instead of the relatively mobile Hquids and 

 gases form the principal mass of the body, keeping in mind meanwhile 

 the slow rate of chemical change in S(jlids compared with the change 

 in substances in a finely divided condition, such as liquids and gases. 

 If the solids predominated, the rate of the chemical change, upon 

 which the active life of animals depends, would be greatly retarded, 

 and animals, including man, would be stolid beyond comprehension. 

 Furthermore, we must not overlook the fact that animals are not main- 

 tained solely by substance, because substances are also carriers of en- 

 ergy, substance and energy never being separated. The living animal 

 is not a producer: it can make neither substance nor energy, nor is it 

 a kind of energy; it is solely a transfonncr, a chemical engine which 

 changes the form of suljstance and chemical energy and produces new 

 combinations from the old. The living plant transforms energy and 

 inorganic substance, from the air, water, and earth, into complex 

 chemical compounds, and thus concentrates powerful chemical energy 

 in such a form that the animal, by a further change, is able to set it 

 free and to utilize it. Sugar, starch, and gluten are familiar examples 



