398 SPECIAL HISTOLOGY. 



circumstances appear contracted, the medullary sheath grumous, 

 the axis-cylinder more opaque and somewhat diminished, in 

 chromic acid yellowish, hut in other respects exactly as above 

 described. In the acoustic nerve of the Sturgeon, Czermak, by 

 means of corrosive sublimate, has demonstrated, in dividing 

 nerve-fibres, the existence, also, of bifurcating axis-cylinders. 

 Iodine also or iodine combined with aqueous hydriodic acid 

 (Lehmann) act very powerfully. In quite recent nerves it 

 instantaneously renders the medullary sheath wholly grumous, 

 and, not only isolates numerous, somewhat shrunken axis-fibres, 

 for a considerable length, but renders them in many nerve- 

 fibres very distinct in situ, and usually appearing convoluted 

 or serpentine. Hydrochloric-, sulphuric-, and fuming nitric 

 acids, in certain cases, also render the axis-cylinders apparent 

 (Lehmann). 



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

 differing from common fibrin, and from the fibrin of the muscles. 

 The chemical nature of the axis-cylinder is difficult of investi- 

 gation, because it cannot be obtained in an isolated form in 

 large quantity ; something, nevertheless, may be learned from 

 microchemical reaction as lias been shown by Lehmann and 

 myself. In concentrated acetic acid it swells up considerably, 

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

 continuously for several minutes, although pale, it always remains 

 unchanged. 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 (potass, 

 soda, ammonia), in the cold, attack the axis-cylinder but slowly, 

 though in soda it instantaneously becomes very pale and swells 

 up to O004 — 0*005 or even O'OOG'". Longer immersion in 

 soda dissolves it, and the same thing takes place upon its being 

 boiled, soon after the commencement of ebullition 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 albumen. 

 Treated with nitric acid and potass the axis-cylinder is rendered 

 yellow (xanthoproteinic acid) and maybe seen spirally contracted, 

 within the nerve-fibres, which are also shortened, but not to the 

 same extent. On the other hand it is not coloured by sugar and 

 concentrated sulphuric acid, which redden coagulated albumen, 

 at most acquiring a yellowish or pale-reddish hue. In water the 



