THE MUSCULAR SYSTEM. 431 



supervene immediately after death, and then pass away with such rapidity 

 as to be scarcely observable. 



Experiments. Brown-Sequard took five rabbits, and killed them by 

 removing their hearts. In the first, rigidity came on in 10 hours, and 

 lasted 192 hours; in the second, which was feebly electrified, it com- 

 menced in 7 hours, and lasted 144; in the third, which was more strongly 

 electrified, it came on in two, and lasted 72 hours; in the fourth, which 

 was still more strongly electrified, it came on in one hour, and lasted 20; 

 while, in the last rabbit, which was submitted to a powerful electro-gal- 

 vanic current, the rigidity ensued in seven minutes after death, and 

 passed away in 25 minutes. From this it appears that the more powerful 

 the electric current, the sooner does the rigidity ensue, and the shorter 

 is its duration; and as the lightning shock is so much more powerful 

 than any ordinary electric discharge, the rigidity may ensue so early 

 after death, and pass away so rapidly as to escape detection. The in- 

 fluence exercised upon the onset and duration of post-mortem rigidity 

 by causes which exhaust the irritability of the muscles, was well illus- 

 trated in further experiments by the same physiologist, in which he found 

 that the rigor mortis ensued far more rapidly, and lasted for a shorter 

 period in those muscles which had been powerfully electrified just before 

 death than those which had not been thus acted upon. 



The occurrence of rigor mortis is not prevented by the previous exist- 

 ence of paralysis in a part, provided the paralysis has not been attended 

 with very imperfect nutrition of the muscular tissue. 



The rigidity affects the involuntary as well the voluntary muscles, 

 whether they be constructed of striped or unstriped fibres. The rigidity 

 of involuntary muscles with striped fibres is shown in the contraction of 

 the heart after death. The contraction of the muscles with unstriped 

 fibres is shown by an experiment of Valentin, who found that if a gradu- 

 ated tube connected with a portion of intestine taken from a recently- 

 killed animal, be filled with water, and tied at the opposite end, the 

 water will in a few hours rise to a considerable height in the tube, owing 

 to the contraction of the intestinal walls. It is still better shown in the 

 arteries, of which all that have muscular coats contract after death, and 

 thus present the roundness and cord-like feel of the arteries of a limb 

 lately removed, or those of a body recently dead. Subsequently they 

 relax, as do all the other muscles, and feel lax and flabby, and lie as if 

 flattened, and with their walls nearly in contact. 



Actions of the Voluntary Muscles. 



The greater part of the voluntary musclss of the body act as sources 

 of power for removing levers the latter consisting of the various bones to 

 which the muscles are attached. 



Examples of the three orders of levers in the Human Body. 



.All levers have been divided into three kinds, according to the relative 



