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actions, although ever so often repeated ; while exertion of muscles 

 beyond their habitual operations, even Avith long intervals of rest, 

 will augment their magnitude and power to an extent, that it is 

 difficult to limit. This law of muscular action applies equally to 

 the voluntary and involuntary muscles. The heart, the dia- 

 phragm, and the muscles so constantly employed in speech in the 

 motions of the eyes and lips, gain no additional bulk during life, 

 unless exerted to an unusual degree. 



As examples of a diiFerent kind, I may mention the enormous 

 bulk the anterior muscles of the' thigh arrive at in old stage- 

 dancers, and the great strength the muscular parts of inter- 

 nal organs acquire, when there exists any obstruction to the expul- 

 sion of their contents. 



A most extraordinary example of the last kind came undei- 

 my knowledge some months ago, in which the left ventricle of 

 the heart, in consequence of a diseased state of the aortic semi- 

 lunar valves, had attained a degree of power by the constant 

 efforts it had to make, so disproportionate to the strength of the 

 arteries, that the smaller branches of the latter were ruptured in 

 several parts of the body, and coagula of blood formed, espe- 

 cially in the substance of the liver, and behind the peritoneum. 

 The tunic of the liver at length gave way, and the patient 

 died, from the quantity of blood, that was shed into the cavity 

 of the abdomen. 



Another law of muscular action deserves to be noticed. Mus- 

 cles lose power and bulk by disuse ; but what would be disuse, 

 in one case, would not constitute it in another ; or, in different 

 words, in proportion to the frequency, with which a muscle is 

 intended to act, the necessity for its exercise exists, in order to 

 prevent its degeneracy. There are some muscles, in the human 



