HISTORY AND METHODS OF INVESTIGATING. 7 



stopped. Iii 1870 Guddcn made use of this fact, and proposed 

 a new method of investigation, which promises well for the 

 future. For example, after the extirpation of an eye he followed 

 up the resulting atrophies in the brain with sections, etc., and 

 found the proximal central ending of the optic nerve. On 

 whatever part of the brain he experimented and afterward 

 examined by sections, he brought to light new and important 

 facts. Besides Gudden, we owe much to Mayser, Ganser, Forel, 

 Monakow, and Lowenthal for important knowledge gained by 

 this method concerning the course of fibres in the spinal cord, 

 the method of origin of different cranial nerves, the course of 

 the lemniscus in the brain, and much more besides. 



Occasionally cases present themselves where nature has 

 performed Gudden J s experiment on human beings ; thus, I was 

 once able to examine the atrophic nerve-tracts caused by the 

 intra-uterine amputation of an arm, and to trace them high up 

 into the spinal cord. At another time I had an opportunity to 

 examine the nervous system of a child who had suffered an 

 extensive softening of the cortex of the parietal lobe, either 

 before or just after birth. The crossed pyramidal tract in the 

 spinal cord was entirely wanting. If division of the peripheral 

 nerves occur later in life, as in amputations, the central changes 

 are not so marked that we can trace out the course of nerve- 

 tracts in the spinal cord or brain. Friedlander and Krause, 

 however, have cleared up the structure of the spinal nerve-roots 

 and of the spinal ganglia by the study of these " amputation 

 (spinal) cords." 



Our knowledge of the course of fibres has advanced con- 



O 



siderably by means of the study of secondary atrophies and 

 degenerations. Still greater advances have been made, however, 

 by a method based upon the study of the development of the 

 medullary sheath. 



P. Flechsig deserves the credit of introducing this method 

 of investigation, which to-day appears to me to be the most 

 promising of all methods in use. 



