CHAP. IX.] THE CONTRACTILE TISSUES. 349 



passu with the physical phenomena of work, heat, and electrical 

 disturbance, which are in some fashion linked to them; or whether 

 the contraction of a muscle is not rather like the firing of a gun, 

 in which the progress of the bullet affords no clue whatever to the 

 course of the explosion. 



Methods of Since then the chemical history of any event in the 



the chemistry life of muscle rests on an analysis of chemical constitu- 

 of Muscle. ti on before and after the event; and since certain of the 



constituents of muscle may be exhaled into the surrounding medium ; 

 it is clear that the chemistry of living muscle comprises two lines of 

 enquiry : 



1. Into the chemical composition of the muscle itself. 



2. Into the chemical composition of the medium surrounding 



the muscle. 



These have for the most part been carried on independently; and 

 the latter has, beyond question, led to the more important results. 

 The enquiry into the chemical composition of the medium sur- 

 rounding muscle has been followed under two sets of conditions, 

 not however essentially different : the simpler, in which the muscles 

 are exposed to the air as a medium; the more complex, in which 

 the muscles remain in the body, or in which the blood is the surround- 

 ing medium. In the latter circumstances the enquiry is complicated 

 by the occurrence of institutional changes. Finally, when muscles 

 are examined while still within the body there are two ways of 

 obtaining a knowledge of the changes in their surrounding medium, 

 viz. by contrasting before, during, and after a muscular act, 



1. The blood of muscle, 



2. The general excreta. 



While this summary includes all the methods of muscular chemistry, 

 it is necessary to state that they have not been equally applied to 

 living muscle in each of its three possible conditions, the resting, the 

 active and the moribund. The latter two conditions have been most 

 freely investigated, and it will be convenient to describe the results of 

 their investigation together, since they have much in common ; and 

 before the results of the examination of the normal state of rest are 

 stated. 



THE CHEMICAL CHANGES OF CONTRACTION AND KIGOR. 



A. Changes in the chemical composition of muscle itself. 



Changes in the gaseous constituents 1 . 



Apparatus. The air pump, which has proved so valuable a means of 



research in the chemistry of the blood, has been also 



The first rudimentary attempt at the gaseous analysis of muscle which the 

 author has met with, is described in a memoir sur V Irritability, by Girtanner, contained 



