52 HUMAN PHYSIOLOGY. 



As shown by an analysis of the blood flowing to and from the 

 resting muscle, it has, while passing through the capillaries, lost 

 oxygen and gained carbon dioxid. The amount of oxygen absorbed 

 by the muscle (nine per cent.) is greater than the amount of CO 2 

 given off (6.7 per cent.). There is no parallelism between these two 

 processes, as CO 2 will be given off in the absence of oxygen, or in an 

 atmosphere of nitrogen. 



In the active or contracting muscle both the absorption of oxygen 

 and the production of CO 2 are largely increased, but the ratio existing 

 between them differs considerably from that of the resting muscle, 

 for the quantity of oxygen absorbed amounts to 11.26 per cent., 

 the quantity of CO 2 to 10.8 per cent. (Ludwig). Moreover, in 

 a tetanized muscle the quantity of CO 2 given off may be largely in 

 excess of the oxygen absorbed. From these facts it is evident that 

 the energy of the contraction does not depend upon the direct oxida- 

 tion of certain substances, but upon the decomposition of some un- 

 stable compound of high potential energy, rich in carbon and oxygen. 

 When the muscle is active, its tissue changes from a neutral to an 

 acid reaction, from the development of sarcolactic and possibly phos- 

 phoric acids. The amount of glycogen present in muscle (0.43 per 

 cent.) diminishes, but muscles wanting in glycogen, nevertheless, 

 retain their power of contraction. Water is absorbed. The amount 

 of urea is not materially increased by muscular activity, unless it is 

 excessive and prolonged, and then only in the absence of a suffi- 

 cient quantity of non-nitrogenized material. Coincident with muscle 

 contraction, the blood-vessels become widely dilated, leading to a 

 large increase in the blood-supply and a rapid . removal of products 

 of decomposition. 



Rigor Mortis. A short time after death the muscles pass into a 

 condition of extreme rigidity or contraction, which lasts from one to 

 five days. In this state they offer great resistance to extension, their 

 tonicity disappears, their cohesion diminishes, their irritability ceases. 

 The time of the appearance of this post-mortem or cadaveric rigidity 

 varies from a quarter of an' hour to seven hours. . Its onset and 

 duration are influenced by the condition of the muscular irritability 

 at the time of death. When the irritability is impaired from any 

 cause, such as disease or defective blood-supply, the rigidity appears 

 promptly, but is of short duration. After death from acute diseases, 

 it is apt to be delayed, but to continue for a longer period. 



