516 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1917. 



is that which considers the de/pendetwc of the animal upon its en- 

 vironment, and at the same time orients it in the gamut of energies 

 and substances. Many phases of this discussion, though elementary 

 and for this reason easily overlooked, are yet of fundamental impor- 

 tance. Every boy who has kept pets in confinement, and who has 

 had the responsibility of caring for them' and every one who has 

 cared for domestic animals, knows what constant attention must be 

 given to keep them supplied with food, water, shelter, and other 

 " necessities of life." 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 isolation which will prevent an animal from securing 

 any " vital necessity " as air — when sealed in a vessel ; or food — when 

 locked ujD 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 con- 

 ditions determine and control the existence and welfare of all wild 

 animals. The animal is not self-sustaining, but requires a constant 

 intake of energy and substance from its environment. Chemical 

 methods will readily show the source from which the materials com- 

 posing 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 of the earth and constitute from 50 

 to 95 per cent of the bulk of the animal's body, showing that a rela- 

 tively large quantity of this substance is essential to all living ani- 

 mals; the abundant gaseous element was derived from the atmos- 

 phere, 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 relatiA^ely mobile liquids and gases form the principal mass of 

 the body, keeping in mind meanwhile the slow rate of chemical 

 change in solids compared w^ith the change in substance in a finely 

 divided condition, such as liquids and gases. If the solids predomi- 

 nated, 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 maintained solely by sub- 

 stance, because substances are also carriers of energy, substance and 

 energy never being separated. The living animal is not a froditcer — 

 it can make neither substance nor energy — nor is it a kind of energ}' ; 

 it is solely a traimformer^ a chemical engine which changes the form 

 of substance 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 com- 



