May 28, 1897.] 



SCIENCE. 



827 



from the posterior epithelium of the iris. 

 There are other observations of similar 

 purport. The acceptance of this inference, 

 however, seems to me to involve such diffi- 

 culties that we may reasonably expect that 

 further investigations will aiford more sat- 

 isfactory explanations of these curious and 

 puzzling phenomena of regeneration. Of 

 much interest and significance are the so- 

 called atavistic regenerations, where the 

 regenerated part assumes characters be- 

 longing not to the variety or species in 

 which it occurs, but to some ancestral or 

 allied species. For these and other reasons 

 Driesch refers the pathological regenera- 

 tions to what he calls the secondary self- 

 regulations, by which term he designates 

 those adjustments of artificially induced 

 disturbances which are brought about by 

 factors foreign to the normal development 

 and life of the individual. 



The view advocated by Barfurth seems 

 to me more probable, that the pathological 

 regenerations depend upon cellular proper- 

 ties pertaining to the normal life of the 

 organism. This view is supported by the 

 fact that, with a few probably only ap- 

 parent exceptions, the regenerations con- 

 form to the law of specificity of cells. The 

 pathological regenerations occurring after 

 birth can be referred to the retention, in 

 greater or less degree, of formative powers 

 possessed by the cells preeminently in em- 

 bryonic life. These powers in general tend 

 gradually to diminution or extinction as 

 the individual grows older, although in 

 some cells, such as the covering epithelium 

 of the skin and mucous membranes, this 

 loss of regenerative power with advancing 

 years is scarcely manifest. Even after the 

 cessation of growth the regenerative ca- 

 pacity is not wholly in abeyance under 

 physiological conditions. Bizzozero has 

 studied and classified the various tissues of 

 the body according to the activity of their 

 physiological regeneration. 



In general, the more highly differentiated 

 and specialized a cell, the less is its capacity 

 for regeneration ; but we now know that such 

 differentiation is attended with less sacri- 

 fice of its regenerative power than was once 

 supposed. Even such highly specialized cells 

 as those of striped muscle are capable of 

 regeneration. Indeed, in higher animals 

 the nerve-cells seem to be the only ones inca- 

 pable of proliferation, and even this is not 

 certain, for there are competent observers 

 who claim that these cells may multiply, 

 although there is no evidence that in the 

 higher animals they can give rise to func- 

 tionally active new nerve-cells. The ease 

 with which a part of the nerve-cell, 

 namely, its axis-cylinder process, can be re- 

 generated is well known. 



The cell-proliferation in regeneration is 

 attributed to the removal of resistance to 

 growth in consequence of the defect result- 

 ing from loss of tissue. It has been pointed 

 out, especially by Ziegler and by Ribbert, 

 that not only cells in the immediate neigh- 

 borhood of the defecb multiply, but like- 

 wise those at such a distance that it is diffi- 

 cult to suppose that the latter have been 

 directly influenced by the loss of tension in 

 the tissues caused by the defect. Ziegler 

 refers the proliferation of the distant cells 

 to compensatory hypertrophy, and Eibbert 

 attributes it to hypersemia resulting from 

 the presence in the defect of foreign ma- 

 terials, such as extravasated blood, exuda- 

 tion and necrotic tissue. 



We are brought here, as we were in the 

 consideration of the compensatory hj'per- 

 trophies, to one of the most fundamental 

 and important questions in pathology — the 

 causes of pathological cell-growth. The 

 interpretation of many pathological pro- 

 cesses as adaptive or not hinges often upon 

 opinions held concerning the underlying 

 causes of cell-proliferation. The main 

 question at issue is. How far is one willing 

 to go in attributing cell-growth to primary 



