.164 THE POPULAR SCIENCE MONTHLY. 



of organs and structures that have thus followed a perfectly normal 

 course?" we are soon able to discover that there exists between 

 the developed organs and the external stimuli which provoked their 

 development a mutual relation of such a kind that one is perfectly 

 adapted to the other; in a perfectly natural state, physiological organ- 

 isms are nicely adjusted to the external conditions surrounding them, 

 in which it is natural for them to live, and which require of the organs 

 developed just such functions as their formation and power adapt 

 them to perform. Adaptation of the organism to its environment is, 

 therefore, the grand purpose of the peculiarities of structure observed 

 in diiferent animals and plants. It is almost needless to present illus- 

 trations ; they occur without number, and are quite apparent to the 

 most superficial observer. The digestive organs are diflerently con- 

 structed in the herbivorous and carnivorous animals, and are thereby 

 adapted to the different kinds of food on which the animals subsist. 

 The gills of lish and the lungs of mammalian quadrupeds are struct- 

 urally and functionally unlike ; the differences adapting the breath- 

 ing-apparatus of each animal to the particular kind of resjDiratory 

 medium in which it is to live. And so of all other organs. 



Now, if, instead of permitting the organism to remain living in its 

 natural state, we change the surrounding natural conditions to others 

 that are unnatural, the action of these latter will excite in the organ- 

 ism corresponding unnatural reactions : at first an unnatural modifi- 

 cation of function will ensue ; and in time, if the modified functions 

 are in this manner continued, we observe a corresponding modification 

 of structure to follow. But the modifications of structure, thus in- 

 duced, are nothing else than organize diseases ; they are departures 

 from the physiological standard of health. And if we ask, " What is 

 the conservative use and designed jiurpose of these unnatural devia- 

 tions?" the answer is, that the modifications of structure adapt the 

 affected organs to modified functions that they have been called upon 

 to perform^ and mould the organism to new conditions that have been 

 brought to act upon it j just as variation in the physiological construc- 

 tion of different animals adapts them to the vai-ious differences of sur- 

 rounding media in which they are designed to live. Pathology, there- 

 fore, is really nothing else than modified physiology. Physiological 

 development is the evolution of organs and the growth of organisms 

 under the impression of natural external conditions; pathological 

 development is the evolution of organs and the growth of organisms 

 under the impression of wnnatural external conditions. Adaptation 

 of structure to function of organisms to surrounding media is the 

 designed conservative purj)ose of both kinds of growth. 



Furthermore, as no two human organisms ar ever, in any particu- 

 lar, precisely similar, and as between organisms that have followed a 

 strictly physiological development, and those whose development has 

 been decidedly pathological, there are stiil others of intermediate 



