50 NERVOUS SYSTEM. 



while this question is so important that it can hardly be neg- 

 lected in studying the physiological anatomy of the nerve- 

 centres, it is one concerning which it seems impossible to ex- 

 press a positive and definite opinion. 



Connection of the Nerve-cells with the Fibres and with 

 each other. Although the mode of connection of the nerve- 

 cells with the fibres and with each other is one of the most 

 important, in its physiological bearings, of all the points 

 connected with the minute anatomy of the nerve-centres, it 

 is impossible, in the present state of our anatomical knowl- 

 edge, to answer the questions involved in a manner entirely 

 satisfactory. This statement is made after a thorough study 

 of the investigations of the most reliable modern observers, 

 among whom may be mentioned Stilling, Lockhart Clarke, 

 Kolliker, K. "Wagner, Jacubowitsch, Yan der Kolk, Deiters, 

 J. Dean, and Schultze, as the most prominent, with many 

 others who have investigated the subject more or less success- 

 fully. 1 A full discussion of the different opinions and the 

 methods of investigation that have been employed would be 

 out of place in this work. The difficulties in the way of 

 arriving at positive information upon these questions are the 

 following : 



1. The nerve-cells and their prolongations are so delicate 

 and easily torn that they cannot be isolated and followed for 

 any considerable distance, and theoretical considerations are 

 constantly required to fill up the deficiencies in actual obser- 

 vation. 



2. In the study of sections of the nerve-centres, the parts 

 must be hardened and afterward rendered transparent by 

 reagents, which must produce more or less change in the 

 structures ; and it seems an anatomical impossibility to make 

 tfrese sections so as to follow out the prolongations of the 



1 Kolliker gives a very full bibliography of the anatomy of the nervous- sys- 

 tem, to which the reader is referred for more extended information. (Elements 

 d'histologie humaine, Paris, 1868, p. 441.) 



