482 MUSCLES. 



towards them : in perfect paraplegia, the sphincters of the rectum 

 and bladder no longer retain their respective contents. Some 

 persons, as Cuvier, and since him Dr. Tiedernann, allow excita- 

 bility to be inherent in muscles, but contend that it is always acted 

 upon through the medium of nerves. It is, however, a mere 

 assumption that, if stimulus can be applied to muscular structure, 

 directly, the presence of nerves is indispensable. Distension acts 

 directly on the muscular fibres; but, with this exception, the 

 functions of muscles are excited intermediately, and therefore 

 through nerves. 



The constant tension of muscles is called their tone. After 

 the retraction of the two portions of a divided muscle, these 

 will contract further on stimulation, and relax again to the 

 length they had after retraction. If overstretched, as by a 

 tumour or other cause, muscles lose much of their forced 

 length immediately on the removal of the cause, but may not 

 completely recover for some time ; and such shortening is said 

 by Prevost and Dumas not to be accompanied by a zigzag di- 

 rection of their fibres, though this appears in them as soon as 

 farther contraction is excited by galvanism. If a muscle not 

 overstretched is divided transversely in several places before its 

 life has ceased, each portion necessarily retracts and necessarily 

 grows harder and heavier. When this is done with fish, it is called 

 crimping, and the retraction is, as might be expected, heightened 

 by immersing the portions in cold water. When fish are to be 

 crimped, they are knocked on the head as soon as caught, that 

 they may crimp the better. This impairment of their nervous 

 powers preserves the power of the muscles, which would other- 

 wise be lost in the struggles of the poor animal : but, if the con- 

 tractility of muscle depended upon nervous energy, it should 

 impair the effects of crimping. This retraction on transverse di- 

 vision takes place only during life or very soon after death, because 

 muscles grow rigid when life has ceased. The latter rigidity 

 is unattended by contraction : it is a mere consolidation, and unfits 

 the fibres for contraction from any cause. Mr. Mayo says that 

 the injection of warm water into the arteries of a muscle induces 

 sudden rigidity. I presume that, like the coagulation of the 

 blood or of albumen, it is a merely chemical change. When death 

 occurs under circumstances which prevent the coagulation of the 

 blood, the rigidity of the muscles is said to be equally prevented. 



Outlines of Human Physiology, ed. 3. p. 38. 



