414 BIOLOGY: GENERAL AND MEDICAL 



As the bone is a product of the periosteum, the loss of 

 much bony tissue in consequence of disease is not in- 

 compatible with its regeneration if the periosteum is 

 not destroyed or too much injured, and it is not unusual 

 for surgeons to strip off a fairly healthy periosteum from 

 a diseased bone, remove the bone, and subsequently find 

 a fair substitute manufactured by the carefully pre- 

 served membrane. 



5. Cartilage. Damage to cartilage is usually repaired 

 by the intermediation of fibre-connective tissue by 

 which the fragments are held together, no new cartilage 

 being formed. 



6. Muscular Tissues. It is improbable that the mus- 

 cular tissue of the mammals undergoes any effective 

 regeneration after injury. Wounds of the unstriated 

 muscle of the uterus and intestines repair through inter- 

 mediate fibre-connective tissue cicatrices. Wounds of 

 cardiac and voluntary muscles usually do the same, 

 though peculiar formations sometimes appear at the 

 injured ends of the voluntary muscle fibres which many 

 interpret to mean that regenerative attempts are in prog- 

 ress. However this may be, the attempts are abortive, 

 little new formation results, and such tissue of supposedly 

 new formation as may be found at the ends of the fibres is 

 distinctly atypical. 



7. The Nervous Tissues. It is not known that the nerve 

 cells can be replaced when destroyed, but the nerve 

 fibres regenerate quite well. The process is not perfectly 

 understood. When a medullated fibre is cut or torn the 

 proximal end degenerates to the next higher "node of 

 Ranvier," and that of the distal end appears to degener- 

 ate altogether. If there is no infection or other un- 

 favorable condition to prevent it, the regeneration of 

 the nerve begins within a few days by an outgrowth 

 from the proximal end. Such outgrowths from the axis 

 cylinders of the proximal ends grow down in the path 

 of the medullary sheaths, extend through whatever 

 cicatricial tissue may be in process of formation, and 



