EELATION OF FOOD TO WORK, AND 281 



dent of proteine, which had been obtained by me from calculation. The 

 actual value of this important constant was found by him to be — 

 Actual value of digestion coefficient of proteine . . 4. 3155 

 Calculated value 4. 8375 



My only object in now j^ublishing an account of the independent ex- 

 periment and calculation made by myself is to coulirm the certainty of 

 the important fact first proved experimentally by Fick and Wislicenus, 

 that the force due to the urea excreted in a given time is not sufficient 

 to provide the actual work that may be done by the muscles in the same 

 time. 



Liebig and his followers, misled by a preconception of the simplicity 

 of nature, assigned to nitrogenous food the duty of providing the force 

 necessary for the production of muscular work, by supplying the waste 

 of muscular tissue; while they supposed the farinaceous and fatty foods 

 to provide the amount of animal heat required by the body. 



The opponents of Liebig have fallen into the opposite error, and deny 

 that nitrogenous food contributes any portion of the force employed in 

 muscular work. 



The truth, as is usual, lies between the two extreme hypotheses, and 

 we are now compelled to admit that a given development of force, ex- 

 pressed in animal heat, muscular work, and mental exertion, may be 

 the effect of several, i)erhaps many, supposable supplies of digested 

 food, farinaceous, saccharine, fatty, and albuminous. 



Just as a given algebraical function may be equated to a given con- 

 stant, by the use of a certain definite number of values of its variable 

 quantity, so may a given effect of work in the animal body be produced 

 by certain definite though very different combinations of various kinds 

 of food, the digestion of which follows each its own law, and develops 

 its own amount of force. The number of roots in our equation of life 

 increases the difficulty of solving it, but by no means permits the accept- 

 ance of the lazy assumption that it is altogether insoluble, or reduces a 

 sagacious guess to the level of the prophecy of a quaclr. 



Lavoisier supposed in his earlier investigations that animal heat was 

 developed by the combustion of carbon and hydrogen in the lungs; just 

 as in earlier times it was supposed lo be produced spontaneously in the 

 heart, which was imagined to be so hot as even to burn the hand that 

 should imprudently venture to touch it. 



Li like manner, Liebig and his followers supposed the muscular work 

 to be developed in the substance itself of the muscles that were its in- 

 struments. 



Both of these doctrines are now justly repudiated by physiologists^ 

 and the view proposed in 1845, by Dr. Mayer, of Heilbronn, and recently 

 developed with much ability l)y Mr. C. W. Heaton, of Charing Cross 

 Hospital, in the Philosophical Magazine for May, 18G7, that the blood 

 itself is the seat of all the chemical changes that develop force in the 



