74 PHYSIOLOGY OF MUSCLES AND NERVES. 



muscle. The methods usually employed in chemistry 

 for the separation and isolation of ditferent substances 

 are of no avail in this case, since they essentially alter 

 the nature of the muscle. AVe must, therefore, be satis- 

 fied to assume as certain only that various albuminous 

 bodies occur in the muscle, one of which, called myosin, 

 appears to be peculiar to muscle, and of which others 

 are the non-nitrogenous bodies glycogen and inosit, 

 toofether with a certain amount of fat and a number of 

 salts. It appears somewhat doubtful whether lactic 

 a,cid, which is always present in the muscle, if but in 

 small quantities, is to be regarded as a normal con- 

 stituent of muscle substance, or if it is not rather a 

 product of decomposition. The same may be said of 

 the gaseous carbonic acid which, like the- lactic acid, is 

 probably only formed during the activity of the muscle, 

 and also of the nitrogenous bodies, such as creatin, which 

 are present in small quantities in muscle, and which 

 must probably also be regarded only as the products of 

 the dissolution of the albuminous bodies. 



2. The only conclusion to be drawn from this frag- 

 mentary information is that part of the muscle-substance 

 unites during the activity of the muscle with oxygen, 

 forming, partly carbonic acid, partly less highly oxidised 

 products. That warmth is generated during these pro- 

 jesses of oxidation, as we have above stated, is not sur- 

 prising. To show this generation of warmth, Helmholtz 

 employed the thermo-electric method. An electric cur- 

 rent rises in a circle composed of two different metals, e.g. 

 copper and iron, as soon as both points of contact — the 

 points where the metals meet or are soldered together 

 — acquire unequal temperatures. The strength of this 

 current is proportionate to the ditfereuce in temperature, 



