278 PHYSIOLOGY AND HEALTH. 



CHAPTER VIII. 



Strength of Muscles not always dependent on Size. Strength differs 

 in various Animals, in Man and Insects, and in various Men. 

 Exercise of Muscles increases their Size and Power. Muscles 

 in Limbs that are exercised stronger than those that are not used. 



641. Muscles are, in general, strong in proportion to 

 tkeir size ; but this is not a univcrsal^law. Birds are very 

 strong, but they have not very large muscles. These would 

 add to their weight, and be very inconvenient for flight. On 

 the contrary, fishes have large muscles, yet are not very 

 strong. Living in the water as they do, which is nearly as 

 heavy as themselves, great bulk is no impediment. They 

 move about as well with a large as with a small mass of 

 flesh. 



642. The difference of muscular power in different 

 classes may be shown by comparing man with some in- 

 sects. A man must be more than usually active to be able 

 to jump his own height. A man of ordinary strength can 

 hardly lift more than twice his own weight ; one of the 

 strongest men on record could lift eight hundred pounds. 

 But insects have astonishing strength of muscle. A flea will 

 leap sixty times its own length, and one of the beetles can 

 support uninjured, and even elevate a weight equal to five 

 hundred times that of its own body. If a man were strong 

 and active in the same proportion, he could jump three 

 hundred and forty feet, or more than twenty rods, and lift 

 aoout three and a half tons"" weight. 



643. Among animals of the same kind, especially among 

 men, it may be safely considered that the muscular power 

 corresponds with the size of the muscles. Though all men 

 are endowed with the same muscles, and these "are arranged 

 in the same manner in all, yet it is manifest that aH men are 

 not equally strong, and that their strength is not distributed 

 in the same proportion over the various parts of the body. 



