202 



ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 



numerous in proportion to the size of the fibre. There is every probability 

 that these nuclei continue to act, like the " germinal spots" of the glandular 



Fig. 105. 



A 



Fig. 106. 







Muscular fibres from fetal pectoralis ; 

 A, from Calf at two months ; B, from hu- 

 man fetus of nine months. 



Mass of ultimate fibres from 

 the pectoralis major of the hu- 

 man fetus, at nine months. 

 These fibres have been im- 

 mersed in a solution of tartaric 

 acid ; and their " numerous cor- 

 puscles, turned in various direc- 

 tions, some presenting nucle- 

 oli," are shown. 



follicles or parent-cells, as centres of nutrition ; from which the minute 

 secondary cells, that compose the fibrillae, are developed as they are re- 

 quired. The diameter of the Muscular fibre of the foetus is not above one- 

 third of that which it possesses in the adult ; and as the size of their ultimate 

 particles is the same in both cases, their number must be greatly multiplied 

 during the growth of the structure. But we shall find reason to believe, that 

 a decay is continually taking place in the component cells, with a rapidity 

 proportional to the functional activity of the Muscle, and their generation, 

 which occurs as constantly when the nutrient operations proceed in their 

 regular course, is probably accomplished by a development from these cen- 

 tres, at the expense of the blood, with which the muscle is copiously supplied. 



236. From the preceding history it appears, that there is no difference, at 

 an early stage of development between the striated and non-striated forms of 

 Muscular fibre. Both are simple tubes, containing a granular matter, in which 

 no definite arrangement can be traced, and presenting enlargements occasioned 

 by the presence of the nuclei. But whilst the striated fibre goes on in its 

 development, until the fibrillse, with their alternation of light and dark spaces, 

 are fully produced, the non-striated fibre retains throughout life its original 

 embryonic character. 



237. Notwithstanding the energy of growth in Muscular Fibre, and the 

 constant interstitial change which seems to take place in its contents, it is 

 doubtful if it is ever regenerated, when there has been actual loss of substance. 

 Wounds of muscles are united by Areolar tissue, which gradually becomes 

 condensed; but its fibres never acquire any degree of contractility. 



238. The Chemical Composition of Muscular Fibre seems to be very uni- 

 form, from whatever source it is obtained. It is impossible, however, to de- 

 termine it with precision ; on account of the difficulty of completely isolating 

 the substance of the fibres from the areolar tissue, vessels, and nerves, that 

 are blended with them. The proper muscular substance differs from the 

 simple fibrous tissues, in not being resolvable into gelatine by the prolonged 

 action of boiling water; and in being soluble in acetic acid, from which it is 



