70 STRUCTURE OF MUSCLE. 



to keep them in working order. For every development of 

 animal force involves a change of state of the Nervo-mus- 

 cular substance : a certain amount of it ceasing to exist as 

 living tissue, and passing into the condition of dead matter ; 

 and its elements resolving themselves, under the influence of 

 the free oxygen brought to them by the blood, into new combi- 

 nations, which are carried forth from the body as quickly as 

 possible. Consequently, if the ISTervo-muscular tissues be not 

 renewed as rapidly as they are used up, their powers must 

 speedily fail from the progressive loss of their substance. In 

 this particular they are on a different footing from the other 

 elementary parts of the organism ; for although each of these- 

 seems to have a certain term of life, the length of which is 

 in some degree related inversely to its functional activity, 

 those which live the fastest having the. shortest individual 

 duration, and vice versd, there are none which are called 

 upon to give forth their whole vital energy in one effort, and 

 which may thus have their existence as parts of the living 

 organism terminated at any moment by a demand for their 

 peculiar power. 



56. Muscular Fibre presents itself under two forms, which 

 are ordinarily very distinct from each other ; although it is 

 probable that they may ultimately prove to be but modifi- 

 cations of one and the same. The first, which is known as 

 the striated fibre, is that of which all those muscles are com- 

 posed, which constitute what is commonly designated as 

 "flesh" or the "lean" of meat. If any "joint" of meat 

 be even cursorily examined, it will be seen that its whole 

 substance is made up of distinct masses,' held loosely together 

 by areolar tissue ; and these masses, which are known as 

 " muscles," are easily isolated from each other by dissection. 

 Every such Muscle is formed by the union of a number of 

 bundles, having a generally parallel arrangement, which are 

 closely bound together by areolar tissue, and are themselves 

 composed of bundles still more minute, united in a similar 

 manner. These, again, may be separated in the same way ; 

 and at last we come to the primitive fibres of which this 

 tissue is composed. Each of these primitive fibres termi- 

 nates at either extremity in tendinous fibre, which unites 

 with other fibres to form the tendinous cords or bands, that 

 are attached to the points of the skeleton which the muscle 



