100 NERVOUS TISSUE. 



organs, whilst those having thicker walls are almost limited to the 

 ganglia. The investing membrane of the latter is very elastic, so 

 that the cells, without being lacerated, admit of being compressed 

 and expanded, resuming their former shape when the pressure is 

 removed. The processes, like the axis-fibres, are remarkable for 

 their elasticity (R. Wagner, Kolliker). 



The nuclei, which generally occupy the centre of the cells, are 

 for the most part spherical or oval, have sharply defined outlines, 

 and contain clear fat-like matters, amongst which one, or even two 

 roundish or elongated nucleoli may in general be distinguished. 

 The size of the nuclei varies from 0'0015 to 0-008'", whilst the 

 nucleoli measure from 0-0005 to 0-0003"' (Kolliker). 



In addition to the nuclei the nerve-cells contain a tough, semi- 

 fluid mass, which is either colourless, or of a faint yellow hue, and 

 holds in suspension finer or coarser granules. In some cases, and 

 more especially in the stellate* cells of the spinal cord, this dark 

 granular mass is collected into various groups or masses, whilst 

 other portions of the cells appear to be less granular. 



We see from this short description of the morphological con- 

 stituents of the nervous system, that we have to take into con- 

 sideration in the chemical investigation of the nervous mass 

 numerous substances, whose difference is made apparent by their 

 variety of form. We will now consider somewhat more minutely 

 the alterations effected on the above-described morphological 

 elements by the action of various chemical reagents, and then 

 endeavour to give a more general representation of the chemical 

 constitution of nervous matter. 



We have already observed that pure water effects a change on 

 fresh nerves which have been removed from animals immediately 

 after they had been killed. The contents of the nerve-tubes pass 

 into a state resembling that of coagulation, which causes the 

 double contour of the cerebro-spinal nerves to appear more dis- 

 tinct, and a coarsely granular mass to separate itself from the 

 periphery towards the centre, whilst in the centre itself there 

 remains an irregularly twisted intestine-like stripe of a light or 

 pale reddish colour. The nerve-cells are scarcely altered by the 

 action of water, or, at all events, no alteration can be definitely 

 recognised in any part of the cell. (F. P. 15, F. 5.) 



Cold alcohol, since it abstracts water from the nervous and 

 cerebral matter, renders these parts harder and almost brittle, but it 



* [The terms caudate and stellate have been applied to these cells, according 

 as they have one or se veral of the processes or prolongations. G. E. D.] 



