Mat 28, 1897.] 



SCIENCE. 



817 



process nor into all of the physiological 

 properties of the cells concerned to enable 

 us to give a positive answer to the question. 



While we must believe that variation 

 and natural selection combined with hered- 

 ity have been important factors in the de- 

 velopment and maintenance of adjustments 

 to normal conditions of environment, it is 

 difficult to see how they could have inter- 

 vened in any direct way in behalf of most 

 pathological adaptations. 



An illustration will make clear the points 

 here involved. Suppose the human race, 

 or any species of animal, to lack the power 

 to compensate the disturbances of the circu- 

 lation caused by a damaged heart-valve, 

 and that an individual should happen to be 

 born with the exclusive capacity of such 

 compensation. The chances are that there 

 would arise no opportunity for the display 

 of this new capacity, and it is inconceivable 

 that the variety would be perpetuated 

 through the operation of the law of survival 

 of the fittest by natural selection, unless 

 leaky or clogged heart-valves became a 

 •common character of the species. When, 

 however, we learn that the disturbance of 

 circulation resulting from disease of the 

 heart- valves is compensated by the perform- 

 ance of increased work on the part of the 

 heart, and that it is a general law that such 

 prolonged extra work leads to growth of 

 muscle, we see at once that this compensation 

 is only an individual instance of the opera- 

 tion of a capacity which has abundant op- 

 portunities for exercise in normal life where 

 the influence of natural selection and other 

 factors of evolution can exert their full power. 



In a similar light we can regard other com- 

 pensatory and functional pathological hyper- 

 trophies; indeed, I believe, also to a consider- 

 able extent the pathological regenerations, 

 inflammation and immunity, although here 

 the underlying factors are,of course, difierent. 



We may, however, reasonably suppose 

 that natural selection may be operative in 



securing protective adjustments, such as 

 racial immunity, against morbific influences 

 to which living beings are frequently ex- 

 posed for long periods of time and through 

 many generations. 



These considerations help us to explain 

 the marked imperfections of most patho- 

 logical adaptations as contrasted with the 

 perfection of physiological adjustments, al- 

 though I would not be understood to imply 

 that the absence of the direct intervention 

 of natural selection in the former is the sole 

 explanation of this difference. The cells are 

 endowed with innate properties especially 

 fitted to secure physiological adaptations. 

 N"o other weapons than these same cells 

 does the body possess to meet assaults 

 from without, to compensate lesions, to 

 restore damaged and lost parts. But these 

 weapons were not forged to meet the special 

 emergencies of pathological conditions. 

 Evolutionary factors have not in general 

 intervened with any direct reference to their 

 adaptation to these emergencies. Such fit- 

 ness as these weapons possess for these 

 purposes comes primarily from properties 

 pertaining to their physiological uses. They 

 may be admirably fitted to meet certain 

 pathological conditions, but often they are 

 inadequate. Especially do we miss in 

 pathological adjustments that coordinated 

 fitness so characteristic of physiological 

 adaptations. So true is this that the pro- 

 priety of using such terms as compensation 

 and adaptation for any results of patholog- 

 ical processes has been questioned. 



A heart hypertrophied in consequence of 

 valvular lesion does not completely restore 

 the normal conditions of the circulation. 

 Experience has shown that a kidney hyper- 

 trophied in consequence of deficiency of the 

 other kidney is more susceptible to disease 

 than the normal organ. What an incom- 

 plete repair of defects is the formation of 

 scar-tissue, and with what inconveniences 

 and even dangers may it be attended in 



