THE PROPERTIES OF MUSCULAR TISSUE. 141 



preciable increase of oxygen-containing nitrogen compounds 

 in it. As, under the conditions of the experiment, no free 

 oxygen is available, the carbon dioxide must be derived from 

 the breaking down of something present in the muscle; and 

 as the formation of sarcolactic acid varies in amount with 

 that of carbon dioxide, and both increase with the work done 

 by the muscle, it would seem as if the energy set free were 

 obtained by the breaking down of some highly unstable 

 non-nitrogenous energy-yielding matter stored in the muscle. 

 And such a view gains support from the fact that a man 

 doing hard muscular work gives off per hour a great deal 

 more carbon dioxide through his lungs than a man at rest, 

 and does not give off any or very little more nitrogenous 

 waste matter. 



But a muscle placed as above described and made to work 

 passes into rigor sooner than a muscle similarly situated and 

 left at rest : and this shows that work tends to favor the pro- 

 duction of myosin, or rather of its immediate precursor myo- 

 sinogen, in the muscle : so here we get some evidence that the 

 nitrogenous muscle constituents are influenced and altered 

 though not oxidized during work. Further, when a muscle 

 passes into rigor it gives off carbon-dioxide gas, whether it 

 has been worked previously or not; if so situated as to be 

 deprived of all exterior sources of supply, it gives off less 

 when becoming rigid after work than when becoming rigid 

 without having been worked; but the difference is almost 

 accurately accounted for by the greater quantity of carbon 

 dioxide the working muscle had previously given out. This 

 suggests that the chemical phenomena of rigor and of work 

 are essentially alike, being merely carried to an extreme in 

 the former. 



Most of the facts can be accounted for by the supposition 

 that there is in living muscle a store of an unstable substance 

 containing nitrogen, hydrogen, carbon, and oxygen. For this 

 hypothetic substance the name inogen has been proposed. 

 During work inogen is used up and broken into a highly 

 oxidized part, carbon dioxide; an oxidized body containing 

 carbon and hydrogen, as sarcolactic acid (C 3 H 6 3 ); and a 

 third body allied to myosinogen and containing all the nitro- 

 gen and some of the oxygen, carbon, and hydrogen of the 

 original inogen. In the products of this alteration stronger 

 chemical affinities are satisfied than in the original compound, 



