1861.] Conservation of Force applied to Organic Nature. 353 



watches, within the last century, who did not know the conservation of 

 force, were induced to try if they could not keep a machine in motion 

 without any expenditure for getting the motive power. Many of them 

 worked for a long time very industriously to find out such a machine 

 which would give perpetual motion, and produce any mechanical work 

 which they liked. They called such a machine a perpetual mover. 

 They thought they had an example of such a machine in the body of 

 every animal. There, indeed, motive-power seemed to be produced 

 every day without the help of any external mechanical force. They 

 were not aware that eating could be connected with the production of 

 mechanical power. Food they believed was wanted only to restore 

 the little damages in the machine, or to keep off friction, like the fat 

 which made the axles of wheels to run smoothly. Now at first by the 

 mathematicians of the last century, the so-called principle of the con- 

 servation of vis viva was detected, and it was shown that by the action 

 of the purely mechanical powers, it was not possible to construct a 

 perpetual mover ; but it remained still doubtful if it would not be 

 possible to do so by the interposition of heat, or electricity, or chemical 

 force. At last, the general law of conservation of force was dis- 

 covered, and stated, and established ; and this law shows that also by 

 the connection of mechanical powers with heat, with electricity, or with 

 chemical force, no such machine can be constructed to give a per- 

 petual motion, and to produce work from nothing. 



We must consider the living bodies under the same point of view, 

 and see how it stands with them. Now if you compare the living 

 body with a steam-engine, then you have the completest analogy. 

 The living animals take in food that consists of inflammable sub- 

 stances, fat and the so-called hydrocarbons, as starch and sugar, and 

 nitrogenous substances, as albumen, flesh, cheese, and so on. Living 

 animals take in these inflammable substances and oxygen ; the oxygen 

 of the air, by respiration. Therefore, if you take, in the place of fat, 

 starch, and sugar, coals or wood, and the oxygen of the air, you have 

 the substances in the steam-engine. The living bodies give out car- 

 bonic acid and water ; and then if we neglect very small quantities of 

 more complicated matters which are too small to be reckoned here, 

 they give up their nitrogen in the form of urea. Now let us suppose 

 that we take an animal on one day, and on any day afterwards; 

 and let us suppose that this animal is of the same weight the first day 

 and the second day, and that its body is composed quite in the same 

 way on both days. During the time — the interval of time — between 

 these two days the animal has taken in food and oxygen, and has given 

 out carbonic acid, water, and urea. Therefore, a certain quantity of 

 inflammable substance, of nutriment, has combined with oxygen, and 

 has produced nearly the same substances, the same combinations, 

 which would be produced by burning the food in an open fire, at least, 

 fat, sugar, starch, and so on ; and those substances which contained 

 no nitrogen would give us quite in the same way carbonic acid and 

 water, if they are burnt in the open fire, as if they are burnt in the 

 Vol. III. (No. 34.) 2 b 



