STRUCTURAL PLAN OF THE HUMAN BRAIN. 379 



among men of genius, has unquestionably done more than any 

 other man living to enlarge our knowledge of the minute struc- 

 ture of the brain, for we owe to him, besides invaluable re- 

 searches, the invention of an entirely novel method of study, by 

 which a few of the cells of the brain are marked out with the ut- 

 most distinctness by a deep deposit of color, while most of the cells 

 and tissues of the brain are left translucent and lightly tinged. 

 The finest ramifications of these cells can be followed in such 

 preparations under the microscope, yet they* have never been 

 proved to unite with the ramifications of other cells. Another 

 method is that which consists in treatment by chloride of gold, as 

 long employed in histology for tracing the finest thread of nerv- 

 ous substance, yet with this also it has hitherto been impossible 

 to demonstrate any actual continuity of cell with cell. There are, 

 however, certain authorities who still uphold the older view. 

 Thus Adam Sedgwick, guided by certain general theoretical con- 

 siderations as to the laws of cell connection, expects to find the 

 continuity hypothesis re-established. Recently Prof. Dogiel, of 

 the Siberian University at Tomsk, has published an article in 

 Russian, in which he apparently seeks to verify the same hypo- 

 thesis by actual observation, but unfortunately his results are 

 not yet fully accessible to me. The settling of the problem is 

 beset with the greatest difficulties. 



The physiological consequences of the theory of non-continuity 

 reach very far. Thus, if the sensory fibers simply branch within 

 the brain, then there must occur a leap from those fibers to the 

 cells which are to send out the reflex response to the sensation. 

 So in other cases there must be a leap from one cell to another. 

 Perhaps the leap or transfer is comparable to an electric induc- 

 tion. But it is obviously useless to ramble into sheer speculation. 



THE FOURTH DISCOVERY. The zones of His were vaguely 

 recognized by Lowe, but to His belongs the honor of having first 

 clearly recognized them and established their morphological im- 

 portance. There are four zones of His two on each side ; they 

 run the entire length of the brain and spinal cord, except that in 

 the partially aborted end of the latter the zones are imperfectly 

 developed. Each zone is a thickening of the wall of the medullary 

 tube. We distinguish the dorsal and ventral zones. The dorsal 

 zone was termed by His the Fliigelplatte (wing plate) and the 

 ventral zone the Grundplatte (basilar plate), but the new names 

 proposed appear to me preferable. At an early stage of develop- 

 ment the two zones are very clearly marked off from one another ; 

 but after a more advanced stage is reached, although they pre- 

 serve their characteristic differences, their delimitation is far less 

 conspicuous. They persist throughout life, and can be identified 

 in the adult. Thus, for example, in the cerebral region proper, or, 



