THE PHYSIOLOGY OF MUSCULAR WORK 227 



and it is doubtful if a more exact measurement or analysis has 

 been obtained by such experiments limited to a small group of 

 muscles. 



The ergograph is a convenient instrument for demonstrations, 

 but the conditions are so different from those of ordinary life that 

 it is safer to rely upon experience and special experiments, such as 

 those * of Zuntz and Atwater, upon men marching or performing 

 some other kind of general muscular work. 



Upon the physical and chemical changes which occur in an 

 isolated muscle during contraction a vast amount of work has been 

 done. 2 Here it is only necessary to mention briefly those facts 

 which have a bearing upon ordinary muscular work. The ex- 

 tensibility of the muscle is increased during contraction, and its 

 temperature is raised. Even in the resting condition the muscle 

 is about 0-1 to 0'6 warmer than the blood which supplies it, and 

 during contraction an increase of M5 has been observed in the 

 muscles of a dog after the blood vessels had been ligatured. Under 

 normal conditions, however, the rapid circulation of the blood 

 distributes the heat so efficiently that the internal temperature of 

 the body is only raised a degree or two by hard work. 3 



The blood supply is greatly increased in the active muscle ; 

 according to Chauveau and Kaufmann's observations the flow 

 is 4-5 times as rapid as during rest. The causes of this change 

 will be considered later in relation to the effect of exercise upon 

 the heart and circulation. 



The chemical changes are shown by an increased absorption 

 of oxygen and an increased discharge of carbon dioxide ; a muscle 

 paralysed by section of its nerve uses 0'003 c.c. of oxygen for one 

 gramme of its weight per minute, but this is raised to O006 or 

 O020 c.c. by tonic activity. 4 The glycogen of the muscle de- 

 creases, owing apparently to its combustion for the supply of 

 energy. These and other similar questions, including the increased 

 growth of muscle, must be discussed in a later portion of this 

 article, which will deal with the general changes in metabolism 

 during muscular work. 



1 See page 233. 



* See article by Burdon-Sanderson, " Textbook of Physiology," edited by Schafer, 

 1900, vol. ii., p. 352 ; and one by v. Frey iu Nagel's Handbuch der Physiologic 

 des Meiwchen, 1907, Bd. iv., s. 427. 



* See page 243. 



4 Barcroft, Ergebnissc der Physiologie, vii. Jahrgang, 1908, p. 699. 



