534 ANIMAL PHYSIOLOGY. 
If it be true, as it unquestionably is, that a certain region 
of the cortex or other portion of the brain is normal only when 
in relation with others, it follows that mere removal can not 
entirely solve such problems as the function of the different 
parts. Nor does it follow, because a localization, meeting the 
needs of practical medicine and surgery, has been established, 
that therefore we are justified in assuming that a scientific lo- 
calization rests upon the same grounds. Any theory that fails 
to recognize both the interdependence of parts and the resources 
of nature in substituting one part for another functionally, 
overlooks principles of very wide application in biology. We 
must express our conviction that neither ablation, stimulation, 
pathological observation, the results of surgical interference, 
nor the facts of clinical medicine, can any of them singly settle 
such questions. 
The comparative method has been as yet but little used. 
Conclusions in regard to the monkey have been applied not 
only to man but other animals; and that the experiments upon 
dogs should result in changes or the absence of changes, to 
which there is no correspondence in the monkey, has hardly 
been recognized as it should. It is only by the synthetical 
method, as we have so often urged, that even an approximation 
to the truth or a part of it can be attained. Results from one 
method or another, taken alone, may be positively misleading, 
unless interpreted in the light of many other facts. The in- 
terpretation is the difficult portion of the task in the study of 
localization ; but, before we are prepared to formulate a correct 
and comprehensive theory, we must begin lower in the animal 
scale, extend observations over a large number of animals, and 
complete these by pathological and clinical observations on 
man and other mammals. If the spinal cord becomes func- 
tionally what it is in any case largely through the life experi- 
ences of the individual, this must also apply to the brain, hence 
we must look for individual as well as group differences. 
The loss of speech (aphasia), in consequence of lesions in the 
left third frontal convolution, was formerly pointed to as un- 
doubted evidence of localization ; but, the more this subject has 
been studied, the more clearly it has been perceived that even 
in this case the theories of a rigid localization break down. 
The speech-center has had its boundaries extended; and it 
turns out that a vast complex of connections must be consid- 
ered, many of which are not confined to the third frontal con- 
volution or its neighborhood. 
