THE STUDY OF NEUROLOGY 231 



in making their appearance, and in the interval the patient may 

 appear as if unaffected by the experience through which he has 

 just passed. The final "breaking-down," due to prolonged strain, 

 is often similarly postponed, only to come on eventually with great 

 suddenness. 



The fact is often overlooked that there is an analogous "latent 

 period" in the early stages of toxic affections, when the symptoms 

 are masked by this strong tendency on the part of the organism 

 to continue offering an unchanged front in response to the calls 

 of the environment. Thus a patient who is exposed to lead or alcohol 

 may retain the power to use his weakened nerves and muscles for 

 a long period, until finally, under some slight additional strain, 

 complete disability suddenly makes its appearance. 



It is apparently this same intense instinct to present a functionally 

 adequate front to the demands of the environment that enables the 

 hysterical patient whose vision is failing to retain the accuracy of 

 the central field, and guides the brain in the reassertion of its powers 

 after injury. The compensation in many cases is so complete as to 

 leave no trace of the primary loss, although some relatively slight 

 additional lesion may make it clearly evident. This is illustrated 

 by the interesting compensatory relationship between the sensory 

 motor functions of the cerebral cortex and those of the semicircular 

 canals discovered a number of years ago by Ewald. 



It is as difficult to explain adequately why it is that the organism 

 thus seeks to reassert itself on the old lines, in a physiological sense, 

 as it is to tell why the lower animals are able to make good the loss 

 of important parts and organs, even those of the interior of the 

 body, with regard to which the "habit" of restoration cannot have 

 been acquired through evolution. 



Many partial explanations, such as those indicated by Loeb 

 under the name of "tropisms," are indeed of value, but Morgan, 1 

 after reviewing with great care the evidence at hand for the case of 

 the restoration of the lost parts, declares that a satisfactory explana- 

 tion is there impossible. One important reason for arriving at this 

 conclusion is that it is by no means invariably true that in the 

 process of restoration the interests of the organism as a whole are 

 consulted. In repair, as in development, the results are often (from 

 the standpoint of the ordinary observer) monstrous or grotesque. 

 And so, too, in human pathology, the processes of compensation 

 and readjustment seem sometimes to work distinctly toward dis- 

 ease instead of health. Nevertheless, these processes must remain 

 the main subject of our study, and the principles underlying them 

 must be re-stated more and more broadly in physiological and 

 philosophical terms, before a unifying conception can be reached. 



1 Regeneration. 



