452 REGENERATION. 



slowly in extremities with fractured bones). Its matrix extends as far as the 

 lunula, and its total or partial destruction causes corresponding loss of the nail. 

 The eyebrows are changed in from one hundred to one hundred and fifty days, the 

 remaining hairs more slowly. Destruction of the papilla in a hair-follicle prevents 

 regeneration. Cutting accelerates the growth of the hair, although cut hair does 

 not grow longer than uncut hair. After attaining a certain length the hair falls 

 out. The hair never grows at its free extremity. The epithelial cells of the 

 mucous membranes and the glands appear to be subjected to a regular cycle 

 in their utilization and in the regeneration of new cells. In the mammary gland 

 and likewise in the sebaceous glands partial desquamation of secretory cells, and 

 also their regeneration, are evident. The regeneration of spermatozoa takes place 

 through spermatoblasts. In catarrhal conditions increased desquamation and 

 regeneration of epithelial cells take place upon the mucous membranes, together 

 with the appearance of indifferent cell-forms (leukocytes) in large number. The 

 crystalline lens, which represents an invaginated epidermal sac that has become 

 independent, regenerates like epithelial structures. Its matrix is the anterior wall 

 of the capsule, with the single layer of cells present in this situation. If the lens 

 is removed, but with preservation of these cells, regeneration takes place, the 

 cellular elements becoming elongated into lenticular fibers and filling the entire 

 cavity of the empty capsule. The removal of large amounts of water from the 

 body may cause turbidity of the lens. 



3. The blood-vessels exhibit extensive regeneration, which takes place in the 

 same way as the formation of the vessels, but this has already been discussed. 

 There always develop at first capillaries, about which, later on, the characteristic 

 tissue-elements are deposited from without in places that subsequently are to 

 become arteries or veins. In case of injury or permanent occlusion of a vessel, 

 at least the portion to the next collateral vessel is always wholly obliterated, 

 derivatives of the endothelial cells, connective-tissue corpuscles from the vessel- 

 wall and wandering cells being transformed into the spindle-cells of the obliterating 

 cicatrix. On the blood-vessels of young and adult animals blind and solid pro- 

 cesses are present as an evidence of constant obliteration and regeneration of the 

 vessels. The lymphatics behave in the same way as the blood-vessels. After 

 removal of lymphatic glands regeneration may take place, especially when stasis 

 of lymph is present. 



4. The contractile substance of the muscular -fibers may undergo regeneration 

 if destroyed by injury or degenerative processes. The contractile, transversely 

 striated contents of the sarcolemma undergo granular or fibrillar degeneration, 

 or break up into discs or plates, the latter being observed in connection with 

 waxy degeneration of the abdominal muscles in cases of typhoid fever. At the 

 same time nuclei in large number appear within the sarcolemma, as well as in 

 this itself, and the previously contractile contents are converted into cell-proto- 

 plasm. In the course of a few days mitotic cell-division is observed. The proto- 

 plasm exhibits at first fine fibrillary longitudinal striation. From this fibrous 

 tissue of myogenous origin, transversely striated, nucleated fibers may be devel- 

 oped in the course of months. In case of considerable loss of muscular tissue or 

 gaping wounds a fibrous cicatrix forms. In fibers injured through subcutaneous 

 wounds Neumann observed, after from five to seven days, a budhke prolongation 

 of the divided extremities, at first without transverse striation, which, however, 

 appeared, later. Unstriated muscle-fiber may regenerate after injury. The nuclei 

 of the injured fibers divide by karyokinesis and about each newly formed nucleus 

 a new muscle-fiber develops in consequence of the differentiation of the surrounding 

 protoplasm. The fibers divide in the middle of their length. 



5. Immediate reunion of a divided nerve never takes place with immediate 

 restoration of function. If a portion of a nerve- trunk be excised, the peripheral 

 extremity of the nerve degenerates first, the medullary sheath and the axis- 

 cylinder being transformed into cells. The deficiency is soon filled with juicy 

 connective tissue. The process pursued later in the regeneration of nerve-fibers 

 is fully considered on p. 636. It is an especially noteworthy fact that in the 

 peripheral nerves a constant loss by fatty degeneration, associated with consecutive 

 regeneration of fibers, takes place. Regeneration of peripheral ganglion-cells does 

 not occur. On the other hand, v. Voit observed in a decerebrated pigeon, after 

 the lapse of five months, a regenerated nerve-mass in the skull, consisting of 

 medullated fibers and central ganglia. Also, Vitzou has reported the regeneration 

 of destroyed cerebral ganglion-cells after the appearance of karyokinesis in the 

 adjacent cells. Eichhorst and Naunyn found in young dogs in which the spinal 

 cord was divided between the thoracic and the lumbar portion that an anatomical 



