WRY BO WE EAT OUR DINNER? 809 



The camel presents a more interesting phenomenon in his well-known 

 humps. These protuberances consist really of reserve-stores of fat, 

 which the camel uses, not only for keeping up the action of his heart 

 and lungs, but also for producing locomotion in his frequent enforced 

 fasts among the deserts of Arabia or India. The humps dwindle away 

 as he marches, in a manner exactly similar to that of the bear's fat dur- 

 ing his hibernation, only of course much more rapidly, as they have so 

 much more work to perform. 



Finally, it may appear strange that the small amount of food we eat 

 should suffice to carry our large and bulky bodies through all the varied 

 movements of the day. But this difficulty disappears at once when we 

 recollect how large an amount of energy can be laid by dormant in a 

 very small piece of matter. A lump of coal no bigger than one's fist, 

 if judiciously employed, will suffice to keep a small toy-engine at work 

 for a considerable time. Now, our food is matter containing large 

 amounts of dormant energy, and our bodies are engines constructed so 

 as to utilize all the energy to the best advantage. A single gramme 

 of beef-fat, if completely burned (that is, if every atom unites with 

 oxygen), is capable of developing more than 9,000 heat-units ; and each 

 such heat-unit, if employed to perform mechanical work, is capable of 

 lifting a weight of one gramme to a height of 424 metres ; or, what comes 

 to the same thing, 424 grammes to a height of one metre. According- 

 ly, the energy contained in one gramme of beef -fat (and the oxygen with 

 which it unites) would be sufficient to raise the little bit of fat itself to 

 a height of 3,816 kilometres, or about as high as from London to New 

 York. Again, it may seem curious that the food eaten by the anaconda 

 in South America, and stored up in its tissues, should suffice to keep up 

 the action of its heart and lungs for so many months. But then we 

 must remember that it performed very few other movements, most prob- 

 ably, during all that time ; and if we think how small an amount of 

 energy we expend in winding up an eight-day clock, and how infinitesi- 

 mal a part of our dinner must have been used up in imparting to it the 

 motion which will keep it swinging and ticking for one hundred and 

 ninety-two hours, we can easily understand how the large amount of 

 stored-up energy in the snake's muscles might very well serve to keep 

 up its automatic actions for so long a time. 



There are five hundred other little points which this mode of re- 

 garding our bodies at once clears up. It shows us why we are warmer 

 after eating a meal, why cold is harder to endure when we are hungry, 

 why we need so little food when we are lying in bed inactive, and so 

 much when we are taking a walking tour or training for a boat-race, 

 why cold-blooded animals eat so rarely and warm-blooded creatures so 

 often, why we get thin when we take too little food, and why we lay on 

 fat when we take too little exercise. But these and many other ques- 

 tions must be passed over in silence, or left to the reader's discrimina- 

 tion, lest I should make this paper tediously long. It must suffice for the 



TOL. XIT. — 52 



