290 OF MUSCULAR CONTRACTILITY. 



were also marks of violence, and many other suspicious circumstances ; but 

 the prisoner Avas acquitted, chiefly from want of evidence against him. What 

 seemed to indicate that the rigidity was of the ordinary cadaveric nature, was, 

 that there was no evidence of the body having become flexible and again 

 stiffened ; as it would probably have done, had the rigidity been of the spas- 

 modic character. 



V. Energy and Rapidity of Muscular Contraction. 



392. There can be no question that, in the living body, the energy of Mus- 

 cular contraction is determined (other things being equal), by the supply of 

 arterial blood, which the muscle receives. It is well known that, when a 

 ligature is applied to a large arterial trunk in the Human subject, there is not 

 only a deficiency of sensibility in the surface, but also a partial or complete 

 suspension of muscular power, until the collateral circulation is established. 

 It is evident, however, that a portion of this effect is to be ascribed to the 

 interruption in the functions of the nervous trunks, which is due to the same 

 cause ; since muscles, taken from the human body, after the circulation has 

 entirely ceased, retain their contractility for some time. The influence of this 

 supply of arterial blood is twofold ; it supplies the materials for the nutrition 

 of the tissue ; and it furnishes (what is perhaps more immediately necessary) 

 the supply of oxygen required for that metamorphosis of the tissue which is 

 probably an essential condition of the generation of its contractile force ( 377). 

 As this oxygen is taken in through the lungs, and as the greater part of it is 

 thrown off when united with carbon into carbonic acid, by the same channel, 

 we should expect to find a very close correspondence between the amount of 

 muscular power developed in an animal, and the quantity of oxygen consumed 

 in its Respiration : and this is in reality the case. We find, for example, that 

 in Birds and Insects, whose respiration is the highest, the muscular power is 

 greater in proportion to their size than in any other animals. In the Mam- 

 malia, and certain Fishes that might be almost called warm-blooded, it is only 

 in a degree inferior. But in the cold-blooded reptiles, Fishes and Mollusca, 

 the muscular power is comparatively feeble ; though even here we trace gra- 

 dations, which accord well with the relative quantities of oxygen consumed. 

 But in proportion to the feebleness of the power, do we usually find its dura- 

 tion greater ( 376) ; so that it is not so immediately dependent upon the 

 supply of oxygen, in cold-blooded, as in warm-blooded animals. Thus, it is 

 found that Frogs are still capable of voluntary movement, after the heart has 

 been cut out ; they can move limbs which are connected with the trunk by 

 . the nerves alone : and that this power is not altogether due to the blood which 

 may remain in the capillary vessels, is shown by the experiment of Miiller, 

 who found the muscles still contractile, after he had expelled all the blood, by 

 forcing a current of water into an artery, until it escaped from the divided 

 veins. It seems probable that the Muscles of Organic life are less dependent 

 upon a supply of arterialized blood, than are those of Animal life ; for the 

 Heart will continue to contract, when the blood in its vessels is entirely venous, 

 and when the circulation in it has come to a stand. Still the dependence of 

 its action upon a constant supply of arterial blood, is very close ; and in all 

 animals, however different the plans of their circulation, we find a provision 

 for this supply, by a special arrangement of the coronary arteries.* That the 

 heart's action comes to an end much sooner, after the destruction of animal 

 life by pithing, when the coronary arteries have been tied, than when they 

 are left untouched, has been proved by the experiments of Mr. Erichsen.t 



* Dr. M. Hall's Gulstonian Lectures, pp. 23, 24. 

 f Medical Gazette, July 8, 1842. 



