OF THE MUSCULAR SYSTEM IN GENERAL. 425 



muscle and its communication with the circulatory and nerv- 

 ous centres, its integral state, and the action of an exciting 

 or stimulating influence. 



Muscular action can not occur unless the circulation takes 

 place in the muscle; should the arteries or principal veins of 

 a part of the body be tied, its muscular action is considerably 

 weakened. The muscles, in order to act, must also commu- 

 nicate through the nerves, with the nervous centre; the inter- 

 ruption of this communication arrests the muscular action 

 more or less suddenly. It invariably and instantly stops the 

 influence of the nervous centre; but the muscle remains irrita- 

 ble from causes that act on it, or on the nerve to which it is 

 still attached. 



680. The muscle must be in its integral state; the contu- 

 sion of the muscles, the inflammation of their cellular sheaths, 

 the accumulation of fat in the intervals of the fasciculi, &c., 

 are so many tircumstances that more or less oppose -the mus^ 

 cular action. The excessive distention of the muscular fibres 

 is sufficient to prevent their action; this is not altogether the 

 case with respect to their contraction. An extreme degree of 

 heat or cold, the immediate application- of opium on the mus- 

 cles, and many other substances, diminish the muscular irri- 

 tability in general, but have little effect, however, on galvanic 

 susceptibility. 



681. To bring the muscle at all into action, it must be ex- 

 cited by some stimulant. The stimulants of muscular action 

 are: 1. Volition, or the action of the will; it acts on the muscles 

 through the medium of the nerves, but it only serves as a 

 stimulant to certain particular muscles, which for this reason 

 are called voluntary muscles; 2. Emotion or passion which acts 

 by the same means, but the action of which is extended to all 

 the muscles; 3. The irritation of the encephalon, of the spinal 

 marrow, or of the nerves, which in the first case, also acts on 

 all the muscles, but with more or less energy; 4. The stimula- 

 tion of some determined part, of the skin or the mucous mem- 

 brane, more or less remote from the muscles; 5. That of the 

 membrane which immediately, covers the muscles, as the in- 

 ternal membrane of the heart, the cellular sheath of the mus- 



