188 ANNUAL OF SCIENTIFIC DISCOVERY. 



conceive that the radius of this boundary, that is to say, the sphere of 

 activity of each molecule, may be equal to a definite number of times 

 the interval between the several molecules, and thus, belonging to the 

 same order of minute magnitudes as they do, may be equally inap- 

 preciable. To this remark, M. Faye adds in a note that, instead of 

 being an absolute quantity, this radius may depend upon temperature, 

 and he then observes : Thus the repulsive force which acts at all dis- 

 tances in celestial spaces finds itself reduced in the interior of bodies 

 to an action at insensible distances, and consequently, in all that 

 concerns the mechanical action of heat, a special hypothesis, like that 

 of Laplace, is useless, as everything is explained on the supposition of 

 force distinct from Newtonian attraction, but not less general in its 

 operations. Is it not remarkable that we have to seek in the heavens 

 for the essential characteristics of the two great forces which govern 

 the material universe ? 



CONSERVATION OF ORGANIC FORCE. 



In 1842 M. Mayer, guided by his knowledge of the correlation of 

 the physical forces, first deduced the general principles of the conser- 

 vation of organic force, in which he was followed, in 1855, by Prof. 

 Helmholtz. For machines there is necessarily a motive power. The 

 machinists of the last century, unaware of the law of conservation 

 of force, sought to find out perpetual motion, and they thought they 

 had examples in the bodies of every animal, where motion seemed 

 produced every day without any supply of mechanical power. Com- 

 pare, then, living bodies with a steam-engine (and the comparison is 

 accurate) ; they take in food the equivalent of fuel in the form 

 of inflammable substances, as fat ; hydro-carbons, as sugar ; nitrogen- 

 ous substances, as albumen, flesh, cheese, etc. ; and so, also, they take 

 in, by respiration, oxygen. 



Living bodies give off, like the steam-engine, the products of com- 

 bustion. Suppose we weigh an animal on two occasions, and find it 

 exactly the same weight. In the interim the animal must have taken 

 in food and oxygen, and have given out carbon, nitrogen and urea ; 

 therefore, certain quantities of materials have been combined with 

 oxygen, and have produced the same results which would have been 

 produced in an open fire, with this only difference, that oxidation goes 

 on slowly in the human body. For the amount of work to be done, 

 it is immaterial how the process goes on ; the amount of work is the 

 equivalent of the chemical process or combustion performed. When 

 an animal is reposing, heat is produced, and its quantity is equal to 

 the quantity of food digested, or to the amount obtainable by burning 

 that quantity of food. Experiments to prove this are difficult to 

 make, but they have been attempted, and the results obtained are 

 within one-tenth of absolute correctness. 



If the body be not reposing, its muscular exertion is the equivalent 

 of mechanical work. There are many different kinds of muscular 

 work, but the greatest amount of muscular or mechanical work is 

 performed on the treadmill, or in going up a hill, in which the whole 

 Vv r eight of the body has repeatedly to be raised ; in the latter case to 

 ascend the declivity, in the former because the hill, so to speak, or 



