HYPER TR OPHY 1 1 9 



how little has been determined as yet by experiment as to the causes 

 that bring about- hypertrophy. Many of the views are more or less 

 plausible in the absence of direct, experimental evidence, but it 

 remains for the future to decide as to the correctness of all of them. 

 They are valuable as suggestions, in so far as they show the different 

 possibilities that must be taken into account. 



Ziegler first advocated the view, in the first edition of his Le/irbuc/i, 

 that hypertrophy is due to a lessening of the resistance to growth. 

 He thinks that while hyperaemia and transudation may support the 

 new growth, they are never the only cause of the formation of new 

 tissue. While Virchow's view that any injury to the body or to an 

 organ excites proliferation finds support in the work of Strieker and 

 Grawitz, yet the view has been combated by Cohnheim and by Wei- 

 gert, and is no longer held by many pathologists. Ziegler points out 

 that as a result of his own work, and that of his students, traumatic 

 and chemical lesions are not followed at once by new growth of the 

 tissue, but by degeneration of the tissue, and by changes in the cir- 

 culation that lead to exudations. The new growth begins, at the 

 earliest, eight hours after the operation, and generally only after 

 twenty-four hours. Also after mechanical, chemical, or thermal 

 injuries, a long interval elapses before phenomena of growth begin. 

 The injury itself does not appear to produce the growth, but brings 

 about those conditions that lead to cell-multiplication. Ziegler dis- 

 cusses what is meant by the idea of a lessening of the resistance to 

 growth. He himself does not mean by this that hypertrophy depends 

 on changes in the physical conditions, because it is known that living 

 phenomena are the outcome of chemical processes and it is, therefore, 

 a priori probable that the effect is brought about by chemical sub- 

 stances in the fluids of the tissues. These substances affect func- 

 tional actions, and may even bring about regenerative changes. This 

 action of chemical substances on the formative activity of the cell is 

 theoretically possible in either of two ways ; first, chemical substances 

 of definite concentration are set free, or, second, chemical substances 

 are present in the normal condition that prevent proliferation, but if 

 their influence should be counteracted by other substances the condi- 

 tions become favorable to growth. It is known in the case of certain 

 unicellular organisms, that derive their nourishment from the surround- 

 ing medium, that their increase in number may be retarded by the pres- 

 ence of certain chemical substances. It is also known that certain 

 organisms may themselves produce chemical substances that prevent 

 their own multiplication. It is, therefore, at least conceivable that after 

 a part has been injured a new substance may be produced that acts 

 upon and destroys in the organ itself the substances there present that 

 have prevented its further growth. The other interpretation is that 



