Chap, ii.] THE CONTRACTILE TISSUES. 95 



satisfactory evidence of any nitrogen waste at all as the result of a 

 contraction ; and, indeed, as we shall see later on, the study of the 

 waste products of the body as a whole leads us to believe that the 

 energy of the work done by the muscles of the body comes from 

 the potential energy of carbon compounds, and not of nitrogen 

 compounds at all. But to this point we shall have to return. 



§ 61. We may sum up the chemistry of muscle somewhat as 

 follows : — 



During life the muscular substance is continually taking up 

 from the blood, that is from the lymph, proteid, fatty and carbo- 

 hydrate material, saline matters and oxygen ; these it builds up 

 into itself, how, we do not know, and so forms the peculiar complex 

 living muscular substance. The exact nature of this living sub- 

 stance is unknown to us. What we do know is that it is largely 

 composed of proteid material, and that such bodies as myosinogen, 

 myoglobulin, and albumin, being always present in it, have 

 probably something to do with the building of it up. 



During rest this muscular substance, while taking in and build- 

 ing itself up out of, or by means of, the above-mentioned materials, 

 is continually giving off carbonic acid, and continually forming 

 nitrogenous waste, such as kreatin. It also probably gives off some 

 amount of sarcolactic acid, and possibly other non-nitrogenous 

 waste matters. 



During a contraction there is a great increase in the amount 

 of carbonic acid given off, an increased formation of lactic acid, 

 and possibly other changes giving rise to an acid reaction, a greater 

 consumption of oxygen, though the increase is not equal to the 

 increase of carbonic acid, but, as far as we can learn, no increase 

 of nitrogenous waste. 



During rigor mortis, there is a similar increased production of 

 carbonic acid and of some other acid-producing substance, ac- 

 companied by a remarkable conversion of myosinogen into myosin, 

 by which the rigidity of the dead fibre is brought about. 



Tliermal Changes. 



§ 62. The chemical changes during a contraction set free a 

 quantity of energy, but only a portion of this energy appears in 

 the ' work done ; ' a considerable portion takes on the form of heat. 

 Though we shall have hereafter to treat this subject more fully, 

 the leading facts may be given here. 



Whenever a muscle contracts, its temperature rises, indicating 

 that heat is given out. When a mercury thermometer is plunged 

 into a mass of muscles, such as those of the thigh of the dog, a rise 

 of the mercury is observed upon the muscles being thrown into a 

 prolonged contraction. More exact results however are obtained 

 by means of a thermopile, by the help of which the rise of tempera- 



