MUSCLE. 27 



tissue, and has no reference to the actual electrical condition of this 

 tissue. 



The electrical changes in muscle can also be demonstrated without 

 the aid of a galvanometer. Two muscle nerve preparations are made, 

 and the nerve of one preparation A is brought into contact at two 

 points with the muscle of the other preparation B. When the muscle 

 of B contracts, the current of action set up in it acts as a stimulus to 

 the nerve of A ; this stimulus is conducted to the muscle of A which is 

 thrown into contraction. 



Chemical Changes during Contraction. Living muscle is constantly 

 taking up oxygen from the blood and giving off carbonic acid. During 

 contraction it takes up more oxygen and gives off more carbonic acid, 

 and at the same time heat is evolved and lactic acid is formed. The 

 production of acid during muscular contraction can be readily demon- 

 strated in a frog's muscle-nerve preparation ; if the muscle is made to 

 contract vigorously for a few minutes it becomes acid to litmus paper. 

 Another method of illustrating the same fact consists in injecting into 

 the dorsal lymph sac of a frog a solution of acid fuchsin, which is 

 colourless in neutral and red in acid solution. When one gastro- 

 cnemius muscle is made to contract an hour or two after the injection, 

 the contracting muscle becomes red, whereas the resting muscles are 

 not coloured. 



It can be shown that the acid formed is lactic acid by means of 

 Hopkins' test. 



A few drops of an alcoholic extract of muscle, two or three drops of a 

 saturated solution of copper sulphate, and 5 c.c. of strong sulphuric acid are 

 mixed in a test tube and placed in boiling water for a minute or two. The 

 fluid is cooled and a few drops of alcoholic thiophene solution are added ; on 

 warming the solution, a cherry red colour develops if lactic acid is present. 



In all probability, when a muscle contracts the first chemical change 

 taking place is the breaking down of a compound of dextrose with some 

 other substance the nature of which is unknown, the decomposition 

 resulting in the formation of lactic acid ; in the presence of an 

 adequate supply of oxygen, the lactic acid can be subsequently 

 oxidised to carbonic acid and water according to the following 

 equation : 



C 8 H 6 8 + 30 2 = 3C0 2 + 3H,0. 

 lactic acid 



This is shown by the observation that an isolated frog's muscle, 

 when made to contract in an atmosphere free from oxygen, gives off 

 less carbonic acid and contains more lactic acid than when it contracts 

 in an atmosphere containing oxygen. Further, if a muscle which 



