S40 MUSCLE IN A STATE OF REST. [BOOK I. 



General Ths maintenance of this normal or in other words, 



Phenomena the preservation of the life of the tissue from moment 

 of Resting to moment is a physiological act consisting in suc- 



Muscie. cessive and simultaneous degenerations and regene- 



rations of parts. The apparent changelessness of repose depends 

 upon the regularity and equilibrium of many hidden changes. The 

 general nature of these changes is roughly indicated by comparing 

 the constitution of the blood flowing to and from muscles. The 

 blood enters muscle comparatively rich in oxygen and poor in carbon 

 dioxide; it leaves the tissue relatively poor in oxygen and rich in 

 carbon dioxide. Therefore the changes of degeneration and regene- 

 ration proceeding within the muscle are, collectively, changes in which 

 at least carbon and oxygen are implicated ; and further, they are, at 

 least in part, of the nature of oxidations. Hence it appears that a 

 supply of new matter to the tissue is ultimately indispensable. The 

 tissue is the channel of a continuous circulation or migration of matter ; 

 it is the theatre of constant material exchanges. The blood conveys to 

 it the substances which are needed; these are elaborated, rearranged, 

 and converted into other forms within the tissue ; and are finally again 

 cast out into the blood-current. These operations, wrought within the 

 tissue of muscle during repose, are included in the term Nutrition ; 

 which may be denned, in a figure now well known to Physiology, 

 as the sum total of the processes which maintain the * stock ' of the 

 organism at the normal. In reality these internal processes of 

 muscle at rest are but little understood ; most of our knowledge 

 of them is derived by inference from the processes of muscular con- 

 traction. But we may assume that they occur in at least three well- 

 defined stages. In the first, what may be called raw material is 

 received into the tissue and stored up in some proximate modification ; 

 in the second, this store is elaborated into an intermediate form by a 

 process independent of the process of storing ; and in the third stage 

 this intermediate body suffers decomposition into certain ultimate 

 products, some of which, but probably not all, are discharged into the 

 blood. 



The grounds for assuming this threefold process will be understood 

 when the contraction of muscle has been discussed. It may be 

 remarked that it finds an exact analogy in the processes of glandular 

 tissues. 



The transformations of matter within the substance of resting 

 muscle, though the more obvious, are not the sole phenomena of 

 nutrition. Running parallel with them are certain transformations of 

 energy. The energy implied in the mutual affinities of the elemen 

 involved in the transformations of matter, undergoes conversion in 

 energy of other forms during the various nutritive changes. 



What these forms are, is again largely a matter of inference. 

 is unquestioned that heat is the most important. A short time ago 

 electrical inequalities or tensions would probably have been set down as 

 a second form ; but this is no longer admissible. The various mov 



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