EELATION OF FOOD TO WORK, AND 269 



ground thus acquired, our little bridge of knowledge may possibly be 

 extended to embrace the j)lienomena of the geometrical instinct of the 

 bee, or the cunning of the beaver, and our successors may even dare to 

 speculate on the changes that converted a crust of bread or a bottle of 

 ■wine, in the brain of Swift, Moliere, or Shakespeare, into the conception 

 of the gentle' Glumdalclitch, the rascally Sganarelle, or the immortal 

 Falstaff. At present such thoughts would be justly regarded as the 

 dreams of a lunatic, and I must crave your indulgence for having men- 

 tioned them. The history of science is, however, filled with such 

 dreams — some never realized, others converted by time into realities so 

 commonplace that the genius of their originators is habitually forgotten 

 or underrated. 



During childhood and youth the food that we eat is used for the 

 double purpose of building up the tissues of the bones, muscles, brain, 

 and other organs of the body, and of supplying the force necessary for 

 work done, whether mechanical or intellectual. In adult life the first 

 use of food almost disappears, for the bones, muscles, brain, and other 

 organs have alreadj" reached their full development, and act simpl}^ as 

 the media of communication between the food received and the work 

 developed by it. 



Let us take, as illustrations, the muscles and brain, regarded as the 

 organs by means of which mechanical and intellectual work is done. 

 These organs resemble the piston, beam, and fly-wheel of the steam- 

 engine, and, like them, only transmit or store uj) the force communicated 

 by the steam in one case, and by the products of the food conveyed by 

 the blood in the other case. The mechanical work done by the sfeam- 

 engine must be measured by the loss of heat experienced by the steam 

 in passing from the boiler, through the cylinder, to the condenser, and 

 not by the loss of substance undergone by the several parts of the 

 machinery on which it acts. In like manner, the mechanical or intel- 

 lectual AYork done by the food we eat is to be measured, not by the 

 change of substance of the muscles or brain employed as the agents of 

 that work, but simply by the changes in the blood that supplies these 

 organs, that is to say, undergone by the food used in its passage 

 through the various tissues of the body, before it is finally discharged 

 in the form of water, carbonic acid, or urea. 



The Divine Architect has so framed the animal machine, that moves 

 and thinks, that the same blood which, by its chemical changes, pro- 

 duces movement and thought, also repairs the necessary waste of the 

 muscles and brain, by means of which movement and thought are pos- 

 sible; just as if the steam that works an engine w-ere able, without the 

 aid of the engineer, to repair the wear and tear of its friction and waste 

 spontaneously; but no greater mistake is possible in physiology than to 

 suppose that the products of the changes in the blood by which 

 mechanical or intellectual work is done are themselves merely the 



