100 HYPERTROPHY, HYPERPLASIA, METAPLASIA, REGENERATION. 



REGENERATION OF SPECIAL TISSUES. 



Regeneration of the Nerve Tissue. In the nervous system we find no 

 evidence that the ganglion cells are capable of reproduction. Some phases 

 of mitosis are occasionally found in them, although they do not appear 

 to lead to proliferation. But if the essential parts of the ganglion cells,_ 

 including the nuclei, be intact, a restoration may occur of their central 

 as well as their peripheral branches. The fibrous and the neuroglia tis- 

 sue of the central nervous system, on the other hand, may increase, and in 

 this way, even with considerable loss of substance, injuries to the brain 

 and cord may undergo a sort of patchwork repair. 



In the peripheral nerves a considerable regeneration of fibres may 

 take place after injury, when the corresponding ganglion cells are intact. 

 This restoration may be effected in part by fibrous tissue which bridges 

 the damaged region and affords guides or channels along which the axis 

 cylinders may grow out from the uninjured central segments, finding 

 their way to their endings, as in embryonic development they stretch 

 into the tissues far from the ganglion cells in which they originate. The 

 restitution is possible here because the centre of nutrition and at least a 

 limited reparative control in the ganglion cell are intact. 



Further details as to degenerations and regenerations of nerves and 

 nerve tracts may be found in the chapter devoted to The Nervous 

 System. 



Regeneration of Muscle Tissue. Regeneration of smooth -muscle tissue 

 after injury is slight. Mitosis may occur in the cells and preliminary 

 phases of division of the body have been described, but it is doubtful 

 whether, except possibly to a very slight extent, new cells are formed. 

 Such healing as occurs after wounds and other injuries is largely effected 

 by new-formed fibrous tissue. 



A partial regeneration of striated muscle occurs after various form of 

 damage and losses of substance. There may be division by mitosis in 

 the sarcolemma nuclei (Fig. 32) associated with the accumulation near 

 them of granular protoplasm, which becomes striated, either in situ or 

 as independent cells. At the injured end of the muscle fibre a similar 

 process may occur, so that these damaged fibres may be in part restored. 



FIG. 32. REGENERATION OF STRIATKD MUSCLE AFTER INJURY. 



The nuclei of the sarcolemma have proliferated and are surrounded by a small amount of non-striated pro- 

 toplasm. 



If as the result of the injury some of the nucleated protoplasm escapes 

 from the sarcolemma, a similar development of striated cells and cell 

 jnasses may occur. 



