CONSERVATION OF ENERGY 95 



secretions formed, and work done. This work may be either mechanical or mental, or both. The animate and inani- 

 mate kingdoms plainly interact. The plant lays the inorganic world under contribution, and the animal lays the 

 vegetable world under contribution ; but the animal in due time restores to the inorganic or mineral kingdom, 

 in undiminished quantity, the substances abstracted from it by the plant. In hke manner, the energy displayed 

 by the animal is to be regarded as the sum of the potential energy stored up in chemical compounds ; and this in 

 turn is restored to the outer world as heat, which, like the matter, is undiminished in quantity. There is, therefore, 

 a cycle of force and a cycle of matter in living beings. " Animals, like machines, can only move and accomplish 

 work by being continuously supplied with fuel (that is to say, food) and air containing oxygen ; both give off, 

 again, this material in a burnt state, and at the same time produce heat and work. All investigation, thus far, 

 respecting the amount of heat which an animal produces when at rest is in no way at variance with the assumption 

 that this heat exactly corresponds to the equivalent, expressed as work, of the forces of chemical affinity then in 

 action. As regards the work done by plants, a source of power in every way sufficient exists in the solar rays which 

 they require for the increase of the organic matter of their structures . . . : a certain portion of force disappears 

 from the sunhght, while combustible substances are generated and accumulated in plants, and we can assume it 

 as very probable that the former is the cause of the latter. . . . The immense wealth of ever-changing meteoro- 

 logical, climatic, geological, and organic processes of our earth are almost wholly preserved in action by the light 

 and heat-giving rays of the sun. ... In the series of natural processes there is no circuit to be found by which 

 mechanical force can be gained without a corresponding consumption." ^ 



§ 14. Conservation of Energy. 



It is necessary to say a word here regarding the great physical law of the conservation of energy. This law 

 resolves itself into three parts, namely, the conservation of energy, the transformation of energy, and the dissipation 

 of energy. We have examples of the conservation of energy in physiology wherever we have mechanical or physical 

 adaptations which produce a maximum of work with a minimum of power. We have examples of the transfor- 

 mation of energy in the muscles moving the bones, or the heart the blood ; and we have examples of the dissipation 

 of energy in the friction accompanying the movements of both bones and blood. In all the vital, physical, and 

 chemical actions and reactions the law plays a prominent part. 



The interaction of the physical, chemical, and vital forces is thus expressed by Professor Helmholtz : " If a 

 certain quantity of mechanical work is lost, there is obtained an equivalent quantity of heat, or, instead of this, 

 of chemical force ; and, conversely, when heat is lost, we gain an equivalent quantity of chemical or mechanical 

 force ; and again, when chemical force disappears, an equivalent of heat or work ; so that in all these interchanges 

 between various inorganic forces, working force may indeed disappear in one form, but then it reappears in exactly 

 equivalent quantity in some other form. . . . The universe possesses, once for all, a store of force which is not 

 altered by any change of phenomena, can neither be increased nor diminished, and which maintains any change which 

 takes place on it. . . . The force of falling water can only flow down from the hills when rain and snow bring 

 it to them. To furnish these we must have aqueous vapour in the atmosphere, which can only be effected by the 

 aid of heat, and this heat comes from the sun. The steam-engine needs the fuel which the vegetable fife yields, 

 whether it be the still life of the surrounding vegetation, or the extinct life which has produced the immense coal- 

 deposits in the depths of the earth. The forces of man and animals must be restored by nourishment ; all nourish- 

 ment comes ultimately from the vegetable kingdom, and leads us back to the same source. . . . We are thrown 

 back upon the meteorological processes in the earth's atmosphere, on the hfe of plants in general, and on the sun." ^ 

 It would appear from this that living force can generate the same amount of work as that expended in its 

 production. 



§ 15. Protoplasm : its Nature and Function. 



The link which binds the organic to the inorganic, and the living to the non-living, is protoplasm in one form 

 or other. This mysterious life-stuff apparently provides the bridge which connects the inorganic and organic 

 Idngdoms. The approaches to this bridge are numerous, but, unfortunately, not altogether satisfactory or safe. 

 Professor Haeckel says : " The homogeneous, viscid, plasma substance which singly and alone formed the bodies 

 of the first organisms, and even at this day quite alone forms them in the case of the monera, or simplest amoebic 

 forms, is analogous to the tenacious and viscid planetary substance which contains the elements and substance of 

 the young earth, as well as of the other glowing world bodies." Mr, Herbert Spencer, who was one of the advanced 



» Op. cit. ' Op. cit. 



