THE NERVOUS SYSTEM. 353 



and fuming nitric acids, in certain cases, also render the axis-cjlinders 

 apparent (Lehmann.)* 



3. The axis-cylinder consists of a solid protein compound differirig 

 from common fibrin, and from the fibrin of the muscles. The chemical 

 nature of the axis-cylinder is difficult of investigation, because it cannot 

 be obtained in an isolated form in large quantity ; something, neverthe- 

 less, may be learned from microchemical reaction as has been shown by 

 Lehraann and myself. In concentrated acetic acid it swells up conside- 

 rably, but is dissolved with difficulty, and even after it has been boiled 

 continuously for several minutes, although pale, it always remains un- 

 changed. When boiled for a longer time in acetic acid it dissolves, 

 exactly like coagulated albumen, whilst the sheaths and some of the 

 contents remain undissolved. Alkalies (potassa, soda, ammonia), in the 

 cold, attack the axis-cylinder but slowly, though in soda it instantane- 

 ously becomes very pale and swells up to 0-004-0-005 or even 0-006 

 of a line. Longer immersion in soda dissolves it, and the same thing 

 takes place upon its being boiled, soon after the commencement of ebul- 

 lition in the fluid. In fuming nitric acid, it disappears in a short time 

 — less than half a minute, — exactly as is the case with coagulated albu- 

 men. Treated with nitric acid and potassa the axis-cylinder is rendered 

 yellow (xanthoproteinic acid) and may be seen spirally contracted, within 

 the nerve-fibres, which are also shortened, but not to the same extent. 

 On the other hand it is not colored by sugar and concentrated sulphuric 

 acid, which redden coagulated albumen, at most acquiring a yellowish or 

 pale-reddish hue. In water the axis-cylinder is unchanged, even when 

 boiled, in which case it is readily isolated and appears somewhat con- 

 tracted ; by ether and alcohol it is undissolved even by boiling, but 

 shrinks to some extent. The latter effect is produced also by corrosive 

 sublimate, chromic acid, iodine, and carbonate of potassa. Viewing all 

 these reactions together, it might perhaps be stated with certainty, that 

 the axis-cylinder is a coagulated protein compound which, however, dif- 

 fers from fibrin, inasmuch as it is insoluble in carbonate of potassa and 

 solution of nitre, and offers much greater resistance to acetic acid and 

 caustic alkalies. On the other hand, it agrees with the substance of 

 which the muscular fibres are composed, in its elasticity and insolubility 

 in carbonate of potassa, differing from it in its insolubility in dilute 

 hydrochloric acid, and difficult solubility in acetic acid. 



These are the most important facts connected with the axis-cylinder. 

 The conclusion which may be drawn from them, appears to me, to be 

 simply this, that the axis-cylinder is not an artificial product, but that 

 it must be regarded as an essential constituent of the living nerves. 



* [I have always obtained the best preparations by soaking a nerve for six or twelve days 

 in concentrated acetic acid. The axis-fibres can then be readily isolated; but are fragile 

 and devoid of their elasticity. — DaC.J 



23 



