CHAPTER XII 



THE CHEMISTRY OF GROWTH AND REPAIR 

 PROLIFERATION AND REGENERATION 



The factors that incite cells to proliferate, as well as those that 

 cause the cessation of proliferation after it has once started, are too 

 entirely unknown to permit of speculation as to their exact nature. 

 It seems probable, however, that they are, as Ziegler says, "identical 

 with the stimuli which excite or increase functional and nutritive 

 activity," and these are certainlj' in manj'' instances of chemical na- 

 ture. Thus the application of various irritating substances in not 

 too concentrated a form (e. g., painting the skin with iodin) may 

 lead to proliferation without causing discernible degeneration of the 

 cells. Mallory's^ observations on the phenomena of proliferation 

 and phagocytosis show that the same bacterial products which destroj' 

 the cells when concentrated, when sufficiently dilute cause prolifera- 

 tion of similar cells. Carnot and Lavlievre^ have obtained evidence 

 that actively growing kidney tissue, whether fetal or adult regener- 

 ating kidney, contains something which is capable of stimulating 

 growth of renal epithelium when injected into other animals. Numer- 

 ous dyes are known to stimulate cell growth greatly, {e. g., the growth 

 of epithelium into oils containing sudan III, etc.) and sometimes seem 

 to lead by virtue of this fact to cancer growth (e. g., cancer of the bladder 

 in dye workers). Chemical products from decomposition of vegetable 

 matter have a particularly active stimulating effect, so that what 

 seem to be true cancers have been experimentally produced by paint- 

 ing the ears of rabbits with tar (Yamagiwa). Manj^ other instances 

 of proliferation in response to chemical stimuli might be cited, 

 but in nearly all cases it is extremely difficult to determine that 

 the proliferation is not, after all, reparative in compensation for 

 degenerative changes, and, therefore, possibly obeying some other 

 biological law than that of a simple reaction to a chemical stimulus. 



Perhaps the most striking example we have of growth stimula- 

 tion by chemical agencies is furnished by the proliferation and hyper- 

 trophy which take place in the uterus^ and mammary gland during 

 pregnane}'. The sanu; phenomena can be produced by injecting the 

 lipoid fraction of extract of placenta and corpus lutcum (Frank).* 



1 Jour. Exp. Med., 1900 (5), 15. 

 -' Arch. M('d. E.xper., 1907 (19), 388. 



■'See Leo Loeb, Jour. Amer. Med. Assoc, 1908 (50), 1897; 1915 (04), 726. 

 * Jour. Anier. Med. Assoc., 1920 (74), 47. 



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