CHAPTER XIII. 



VOLUNTARY MUSCLE. 



NECROSIS. 



NECROSIS of muscle may be the local result of mechanical or chemical 

 injury ; it occurs in inflammatory foci, and may follow serious local dis- 

 turbances of the circulation, as from pressure by tumors or cicatrices, etc. 

 The muscle fibres may gradually lose their striatious, become granular and 

 disintegrate, or the muscle substance may become homogeneous and 

 strongly refractile and break into irregular masses. Necrotic muscle 

 fibres are finally removed by the direct action of phagocytes or after 

 various transformations leading to solution (see page 117). 



ATROPHY AND HYPERTROPHY. 



Simple Atrophy. This may occur in old age, in prolonged exhausting 

 diseases, or as a result of pressure from a foreign body, tumors, etc. 

 The muscle fibres grow narrower, the degree of narrowing frequently 

 varying considerably in different parts. They usually retain the stria- 

 tions, but these may be obscured by degenerative changes. The sarco- 

 lemma may become thickened, and there may be a considerable increase 

 in connective tissue between the muscle fibres and bundles. Brown pig- 

 ment particles may accumulate in the atrophied fibres. 



Progressive Muscular Atrophy. This lesion consists essentially in a 

 combination of simple or degenerative atrophy of the muscle fibres with 

 chronic interstitial inflammation, and is sometimes associated with pro- 

 liferative changes in the muscle nuclei. In the earlier stages of the dis- 

 ease the muscles may be pale and soft, but exhibit otherwise to the naked 

 eye but little alteration. Gradually, however, the muscle substance be- 

 comes replaced by connective tissue, so that in marked and advanced 

 cases the muscles are converted into fibrous bands or cords, whose cica- 

 tricial contraction may induce great deformities. 



Microscopical examination shows in the early stages of the disease a 

 proliferation of cells in the interstitial tissue, so that this may have the 

 appearance of granulation or embryonal tissue ; also in some cases marked 

 proliferative changes in the muscle nuclei (Fig. 495), leading to the 

 formation of new cells which may more or less replace the contractile 

 substance within the sarcolemma. The new interstitial tissue increases 

 in quantity and grows denser, and may crowd the muscle fibres apart 



