462 STUDIES IN ADVANCED PHYSIOLOGY. 



determination of these anatomical malformations and their 

 comparison with the observed mental acts, deductions have 

 been arrived at as to the function of the parts affected. 



Second. Occasionally a normal brain is pathologically 

 injured either by compression, as in accidents, by inflam- 

 mation in disease, or by the formation of tumors in certain 

 portions of its structure. It was by noticing the fact that 

 the presence of a tumor in the left frontal lobe of the brain 

 was always associated with the loss of speech that that cen- 

 ter was finally localized in that region. 



Third. Upon animals it has been possible to cut off 

 certain regions of the brain to note the physiological effects of 

 such excisions. It was, for instance, by the extirpation of 

 the occipital lobes of the brain that the center of conscious 

 vision was definitely located. 



Fourth. By stimulation experiments made directly on 

 the cortex of the brain. A new era in brain physiology was 

 ushered in when Fritsch, Hitzig, and later Ferrier, suc- 

 ceeded in producing movements by electrically stimulating 

 certain regions of the cortex of the brain. By subjecting 

 various portions of the cortex to such stimuli and noting 

 what muscles of the body were affected by the motor im- 

 pulses so originated, it was soon relatively easy to map out 

 the motor topography of the cortex, and it is upon these ex- 

 periments that the results in the diagram are based. 



Fifth. For the determination not only of the centers of 

 the brain, but of the nerve fibers which extend from them, 

 two methods of study suggested themselves, (a) In the 

 embryonic development of animals it was found that certain 

 cells and certain nerve fibers developed sooner than others, 

 so that in this way it was possible to give the region and 

 follow the course of certain nerve fibers before neighboring 

 ones with which they might later be confused had de- 

 veloped, (b) A method productive of even more results 

 than this was what was called the Wallerian method, or the 

 method of degeneration. It has already been pointed out. 



