j6 Journal op Comparative Neurology. 



blue, prepared with normal salt solution, into the circulation of 

 a living animal, many of the nerve cells and nerve fibers would 

 be colored blue in a most satisfactory manner. The great draw- 

 back to this method as introduced by Ehrlich was that tissues 

 so stained could be examined only in their fresh state, and even 

 then would soon fade. 



This method was however soon improved by Smirnow (5) 

 and Dogiel (6) who showed that the tissues so stained might be 

 fixed in a saturated watery solution of ammonium picrate, and it 

 was further modified by Bethe (7) who found that ammonium 

 molybdate would convert the very unstable methylen-blue stain 

 into one practically insoluble in water and alcohol. So that 

 tissues stained ititra vitani, with a methylen-blue solution, may 

 now be embedded and sectioned and even double stained with- 

 out losing much of their original blue color. By way of paren- 

 thesis I may here say Uiat, while both of these methods are 

 applicable to the study of the entire nervous system, the Golgi 

 method has been most useful in the study of the central ner- 

 vous system, while the methylen-blue method is now more gen- 

 erally used in the study of peripheral ganglia, peripheral 

 nerves and their endings. 



The results obtained by these methods are so convincing 

 that we are not surprised to find that all parts of the nervous 

 system have been subjected to repeated investigations, since 

 their introduction. Some of the more important results which 

 these investigations have brought to light, are, on account of 

 their bearing on the subject under discussion, worthy of brief 

 mention in these introductory remarks. 



As a result of these investigations we know that the entire 

 nervous system, peripheral as well as central, is like all other 

 tissues of the body built up of anatomical units, which, though 

 they vary greatly in shape and size, are nevertheless to be re- 

 garded as highly differentiated cells. 



Such nerve units consist of a cell body and nucleus and 

 one or several processes. These processes are of two kinds. 

 The one kind essential to each cell, usually becomes the axis- 

 cylinder of a nerve fiber, and as such may attain great length, 



