CAUSES AND PHENOMENA OF MOTION. 39 



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 influence 

 exercised upon the onset and duration of post-mortem rigidity by causes 

 which exhaust the irritability of the muscles, was well illustrated 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 as the voluntary muscles, 

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

 of involuntary muscles with striped fibres is shjown 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 pre- 

 sent the roundness and cord-like feel of the arteries of a limb lately 

 removed, or tho?e 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 muscles 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 position of ' 

 the power, the weight to be removed, and the axis of motion or fulcrum. 

 In a lever of the first kind the power is at one extremity of the lever, the 

 weight at the other, and the fulcrum between the two. If the initial 



