10() HYPERTROPHY, HYPERPLASIA, METAPLASIA, REGENERATION. 



very clear. Regeneration of redbtood cells seems to ^>ccur in the bone, 

 marrow through mitotic division of nnelqated forms. The latter may, 

 under pathological conditions, appear in the vessels in varying numbers 

 (see Part III., Chapter I.); 



Transplantation of Tissue. Transplantation of tissue may be success- 

 fully made from one part of the individual to another or from another 

 individual of the same species. The epithelium of the skin and the vari- 

 ous forms of connective tissue are most readily transplanted and produce 

 new tissue of similar type. The transplantation of gland tissue is less 

 successful, certain glands, such as the mammary gland and thyroid, show- 

 ing some new gland-tissue formation ; while on the other hand, kidney, 

 IrrejV and test icle > douiot, p ro 1 i IV rat e in the new situation, but undergo 

 speedy degeneration and absorption. Nevertheless, with the exception 

 of the skin epithelium the life of the transplanted tissue is usually short 

 and it degenerates and is absorbed, being replaced by adjacent tissues. 1 



THE IMPULSE TO CELL REGENERATION. 



While we can thus summarize the differing capacities of the body 

 cells for regeneration, while we know many of the general conditions 

 under which the impulse to cell proliferation and growth is manifested, 

 while, further, we have learned something of the delicate mechanim 

 through which division is controlled and effected, at the end we must 

 acknowledge that we do not know why cells divide. We may say that 

 it is due to a chemical or a mechanical stimulus, and it certainly may be 

 associated with both, or that increased nutrition favors while innutrition 

 retards cell multiplication ; we may cite direct or remote injury, or talk 

 of the inhibition of organic control, disturbed tissue equilibrium, dimin- 

 ished pressure, etc., but when all is said we are forced to recur to some 

 unknown factor in the inherited constitution of the cell which determines 

 the measure and character of its response to the most varied influences. 2 



1 For a fuller resume of this subject, with bibliography, consult Ziegler'y "General 

 Pathology," Warthin's translation, 1903. 



' 2 Consult in this connection, for bibliography on the formative stimulus, references 

 on the Origin of Tumors, p. 301. 



See also, for summary of a new phase of research and interpretation in the nature 

 of the "formative stimulus" involved in artificially induced cell division and artificial 

 parthenogenesis, Loeb, Am. Jour. Phys., vol. iv., p. 423, 1901, and for a review of 

 recent advances in the knowledge of the cell, Wihon, "Some Aspects of Biological Re- 

 search." The International Monthly, July, 1900. For general bibliography of regen- 

 eration, compensatory hypertrophy, etc.. see Aschoff, Lubarsch and Ostertag's Ergeb- 

 nisse, Jahrg. v. for 1898' p. 22. 



