8oo THE POPULAR SCIENCE MONTHLY. 



ways been accustomed to dine daily from their childhood upward, they 

 felt hungry at the habitual dinner-hour, and they sat down to their five 

 courses with an unquestioning acceptance of the necessity for feeding 

 to prevent starvation. But when I inquired why people who did not 

 eat should starve, why they should not imitate the thrifty anaconda, and 

 take one meal in a twelvemonth instead of three in a day, they appeared 

 to regard my question as rather silly, and as certainly superfluous. Yet 

 I must confess the query seems to me both pertinent and sensible ; and 

 it may be worth while to attempt some answer here in such language 

 as can be understanded of the people, without diving into those pro- 

 found mysteries of formula and equations with which physicists love to 

 becloud the subjects of their investigation. 



A still more startling case than that of the anaconda will help to 

 throw a little light upon the difficult problem which we have to solve. 

 An Egyptian desert-snail was received at the British Museum on March 

 25, 1846. The animal was not known to be alive, as it had withdrawn 

 into its shell, and the specimen was accordingly gummed, mouth down- 

 ward, on to a tablet, duly labeled and dated, and left to its fate. In- 

 stead of starving, this contented gasteropod simply went to sleep in a 

 quiet way, and never woke up again for four years. The tablet was 

 then placed in tepid water, and the shell loosened, when the dormant 

 snail suddenly resuscitated himself, began walking about the basin, and 

 finally sat for his portrait, which may be seen of life-size in Mr. Wood- 

 ward's " Manual of the Mollusca." Now, during those four years the 

 snail had never eaten a mouthful of any food, yet he was quite as well 

 and flourishing at the end of the period as he had been at its beginning. 



Hence we are led to the inquiry — What is the actual function which 

 food subserves in the human body ? Why is it true that we must eat 

 or we must die, while the snake and the snail can fast for months or 

 years together with impunity ? How do we differ from these lower 

 animals in such a remarkable degree, when all the operations of our 

 bodies so closely resemble theirs in general principle ? 



Everybody has heard it said that food is to men and animals what 

 fuel is to a steam-engine. Everybody accepts this statement in a vague 

 sort of way, but until the last few years nobody has been able really to 

 explain what was the common feature of the two cases. For example, 

 most people if asked would answer that the use of food is to warm the 

 body, but this is really quite beside the question : because, in the first 

 place, the use of fuel is not to warm the steam-engine, but to keep up 

 its motion ; and, in the second place, many animals are scarcely per- 

 ceptibly warmer than the medium in which they live. Again, most 

 people show in every-day conversation that they consider the main ob- 

 ject of food to be the replacement of the materials of the body ; where- 

 as we shall see hereafter that its real object is the replacement of the 

 energies which have been dissipated in working. Indeed, there is no 

 more reason why the materials of an animal body should waste away 



