CHAP. IX.] THE CONTRACTILE TISSUES. 381 



three succeeding minutes, restored the muscle almost perfectly. It 

 would seem that so little as 1*8 mgr. of oxygen is sufficient to restore 

 the irritability of a muscle weighing 209 grms. 1 



Analysis of As compared with the changes wrought in the 



the non-gase- gaseous constituents of the blood by the exercise of 



ents arte 11 " musc l e > the changes in the non-gaseous constituents 

 wood of due to the same circumstance are small and less 



muscle. certain. 



It has been stated that during muscular activity, the amount of 

 the aqueous extractive matters removable from muscle diminishes, whilst 

 the alcoholic extractives increase : that whilst glycqgen diminishes, sugar 

 increases and lactic acid makes its appearance ; further that tetanized muscle 

 possesses considerable reducing powers, which we may surmise to be 

 associated with the production of new substances within the muscle. 



Were our knowledge of the chemical composition of the blood complete, 

 we should expect to find variations in the composition of that fluid, after it^ 

 has passed through a muscle, which should be the correlatives of the changes 

 which occur in the muscle itself. In so far as the gases are concerned this 

 has been shewn to be the case. In reference to non-gaseous constituents, 

 our information is, however, of the scantiest character ; it indeed is limited 

 to the two following statements. 



1. During tetanus, blood circulating through muscle becomes charged 

 with reducing substances. 



Alexander Schmidt passed two different quantities of blood free from 

 oxygen through muscle at rest, and through muscle which was tetanized, 

 and then agitated the two specimens of blood with oxygen. He found that 

 the blood which had traversed teteunized muscle took up more oxygen than 

 that which had traversed resting muscle, and from this he concluded that 

 tetanized muscle gives up reducing substances to blood. 



2. During tetanus blood acquires sarcolactic acid (Spiro 2 ). We yet 

 possess very slight information on this point. 



Changes in the medium surrounding muscle as shewn in the 

 analyses of the general excreta of the body. 



The excretions which are modified by muscular exercise are those 

 of the lungs and kidneys. The description .of the methods of 

 collecting and examining these excretions properly belongs to the 

 Chapters on Respiration and the Urine. It will, therefore, merely be 

 necessary here to speak of the methods of experiment having a 

 peculiar bearing on the question of muscular work. 



Effects of As regards the excretion of the lungs, it has long 



muscular ex- been known that the volume of respired air is increased 

 ercise on the .. , . , , * , . 



pulmonary during muscular exertion, and that the proportion 01 



exchanges. carbon dioxide and oxygen involved in the process of 



1 Ludwig and A. Schmidt, Op. cit. pp. 58 and 61. 



2 Spiro, "Beitrage zur Physiologie der Milchsaure." Zeitachrift f. phys. Chemie, 

 Vol. i. (187778) p. 111. 



