116 NERVOUS TISSUE. 



cells does not easily dissolve in acetic acid and in alkalies, although 

 it certainly cannot be regarded as entirely insoluble in them. It 

 may, indeed, bear some resemblance to syntonin, for the cell-mem- 

 brane is insoluble in carbonate of potash, and, as we have already 

 stated, the nerves harden in a solution of this salt. It is worthy 

 of notice in reference to this subject, that the grey, highly cellular 

 substance of the central organs becomes more hardened than the 

 white. 



The nuclei of the nerve-cells, like those of most other cells, are 

 rendered more distinctly visible by acids, whilst they disappear in 

 alkalies, without, however, enabling us to form any exact idea of 

 their chemical nature. 



It appears from the micro-chemical reactions, which have been 

 previously described, that the semi-fluid granular contents of the 

 nerve-cells are much poorer in fat than the pulp of the nerve-tubes ; 

 for after the application of acetic or hydrochloric acid, or other re- 

 agents, we perceive a far smaller quantity of coarse granular fatty 

 matter in them than in the nerve-pulp. This observation would 

 appear to acquire corroboration from the smaller quantity of fat in 

 the grey than the white substance of the brain, provided, indeed, 

 that any definite conclusions can be drawn from analyses of entire 

 portions of the brain. All analysts have found only very little fat 

 in the grey substance, which is so rich in cells, whilst in the fibrous 

 medullary substance there is at least four times as much fat pre- 

 sent. As, moreover, the contents of the nerve-cells are not ren- 

 dered much paler by the application of alcohol or ether, their 

 granular appearance must be owing less to fat than to other mole- 

 cular matters. These granules must not, however, be confounded 

 with those very dark granules, which are insoluble in caustic alka- 

 lies, and which we chiefly see in the nerve-cells which are either 

 stellate or provided with long processes or prolongations. These 

 consist of a substance which is still chemically unknown to us, but 

 which is not very dissimilar to pigment-granules. It would appear, 

 therefore, highly probable from the above observations, that the 

 principal part of the contents of the nerve-cells consists of a partly 

 dissolved, and partly only swollen protein-substance. 



If we now take a glance at the little that is known regarding 

 the composition of the cerebral and nervous masses generally, the 

 following points present themselves to our notice ; we must, how- 

 ever, bear in mind that the cerebral mass contains a large number 

 of blood-vessels and, consequently, a quantity of blood, which must 

 not be included in the analysis. 



