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SCIENCE. 



[N. S. Vol. V. No. 126. 



prefer to say, adaptive, is not accepted by 

 all pathologists, it seems to me the best ex- 

 planation in many cases. But the adapta- 

 tion, if it be such, is here usually of a very 

 imperfect nature, and it is not surprising 

 that it should be so, when one considers the 

 improbability of any mechanism developing 

 under physiological conditions which should 

 be specially fitted to meet the particular 

 morbid changes underlying aneurism and 

 arterio-sclerosis . 



I shall not be able to enter into a consid- 

 eration of the mechanical factors concerned 

 in adaptive pathological processes in blood- 

 vessels, although perhaps in no other field 

 are to be found more pertinent illustrations 

 of the views here advocated concerning 

 pathological adaptations. The whole sub- 

 ject has been studied from the mechanical 

 side most fully and ably by Thoma, whose 

 four beautifully simple histo-mechanical 

 principles are at any rate very suggestive 

 and helpful working hypotheses, even if it 

 should prove, as seems to me probable, that 

 they are too exclusive. I shall call atten- 

 tion in this connection only to the inade- 

 quacy of the old and still often adopted ex- 

 planation of the development of a collateral 

 circulation. The rapidity with which a 

 collateral circulation may be established 

 after ligation of a large artery, even when 

 the anastomosing branches are very small, 

 is known to every surgeon. This was 

 formerly attributed to increase of blood 

 pressure above the ligature, but this rise of 

 pressure has been shown to be too small to 

 furnish a satisfactory explanation, and 

 Nothnagel has demonstrated that there is 

 little or no change in the calibre of arteries 

 coming off close above the ligature unless 

 they communicate with branches arising 

 below the ligature. Von Recklinghausen 

 several years ago suggested a better expla- 

 nation. The bed of the capillary stream for 

 the anastomosing arteries is widened by 

 ligation of the main artery, inasmuch as the 



blood can now flow with little resistance 

 from the capillaries of the anastomosing 

 branches into those of the ligated artery. 

 The result is increased rapidity of blood- 

 flow in the anastomosing vessels. Accord- 

 ing to one of Thoma's histo-mechanical 

 principles, increased velocity of the blood 

 current results in increased growth of the 

 vessel wall in superficies — that is, in widen- 

 ing the lumen. The tension of the vessel 

 wall, which is dependent on the diameter 

 of the vessel and the blood pressure, is, 

 according to Thoma, thus increased ; and,, 

 according to another of his principles, this 

 greater tension results in growth of th© 

 vascular wall in thickness. The changes in 

 the walls of the anastomosing vessels seem 

 to me to be best interpreted as referable to a 

 genuine work hypertrophy, a conception 

 which has already been advanced by Ziegler. 



The pathological regenerations constitute 

 a large group of adaptive morbid processes 

 of the highest interest. Their study has 

 become almost a specialized department of 

 biology, and occupies a very prominent 

 place in the extensive literature of recent 

 years relating to experimental or physiolog- 

 ical morphology. It has revealed, in un- 

 expected ways, the influence of external 

 environment upon the activities of cells, as 

 is illustrated in a very striking manner by 

 Loeb's studies of heteromorphosis. 



Although the capacity to regenerate lost 

 parts must reside in the inherited organiza- 

 tion of the participating cells, there are 

 observations which seem to indicate that 

 in the lower animals this capacity may 

 exist independently of any opportunity for 

 its exercise during any period of the normal 

 life of the individual or species or their 

 ancestors, including the period of embryonic 

 development. This is the inference which 

 has been drawn from Wolfl"'s observation, 

 that after complete extirpation of the ocular 

 lens with the capsular epithelium in the 

 larval salamander a new lens is reproduced 



