46 HUMAN PHYSIOLOGY. 



nitrogenized extractives e. g., urea, uric acid, kreatinin, as well as inorganic 

 salts, have been obtained from the muscle serum. 



Metabolism in Muscles. The chemic changes which underlie the trans 

 formation of energy in living muscles are very active and complex. 



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 

 oxidation of certain substances, but upon the decomposition of some unstable 

 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 phosphoric acids. The amount 

 of glycogen present in muscle (0.43 per cent.) diminishes, but muscles want- 

 ing 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 sufficient 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 appear- 

 ance 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 rigid- 

 ity 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. 



The rigidity appears first in the muscles of the lower jaw and neck; next 



