A HISTORY OF SCIENCE 



of recent periods avails himself of sections of brain 

 tissues of a tenuousness which the early investigators 

 could not approach. 



But more important even than the cutting of thin 

 sections is the process of making the different parts of 

 the section visible, one tissue differentiated from an- 

 other. The thin section, as the early workers exam- 

 ined it, was practically colorless, and even the crudest 

 details of its structure were made out with extreme 

 difficulty. Remak did, indeed, manage to discover 

 that the brain tissue is cellular, as early as 1833, and 

 Ehrenberg in the same year saw that it is also fibrillar, 

 but beyond this no great advance was made until 1858, 

 when a sudden impulse was received from a new process 

 introduced by Gerlach. The process itself was most 

 simple, consisting essentially of nothing more than the 

 treatment of a microscopical section with a solution of 

 carmine. But the result was wonderful, for when such 

 a section was placed under the lens it no longer ap- 

 peared homogeneous. Sprinkled through its substance 

 were seen irregular bodies that had taken on a beautiful 

 color, while the matrix in which they were embedded 

 remained unstained. In a word, the central nerve cell 

 had sprung suddenly into clear view. 



A most interesting body it proved, this nerve cell, or 

 ganglion cell, as it came to be called. It was seen to be 

 exceedingly minute in size, requiring high powers of the 

 microscope to make it visible. It exists in almost infi- 

 nite numbers, not, however, scattered at random 

 through the brain and spinal cord. On the contrary, it 

 is confined to those portions of the central nervous 

 masses which to the naked eye appear gray in color, 



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