G96 DR ROBERT KENNEDY ON THE 



the right moment, as if allowed to act too short, the axis-cylinders appear red, and if 

 too long, the colour is extracted from the myelin. 



An addition to the method, which gives very beautiful results in some cases, is that 

 of rinsing the slide after removal from the safranin solution for a few seconds in a very 

 dilute aqueous solution of eosin. With this addition all parts of the section are stained 

 red, except the axis-cylinders, which stand out in blue, and the clear differentiation thus 

 obtained between the young axis-cylinder and connective tissue fibres is of much 

 advantage. The objection, however, is that the eosin is apt to stain also the axis- 

 cylinders so intensely as to be incapable of removal by the oil of cloves, unless the 

 immersion in eosin is very short, and possibly in all cases some of the finer axis- 

 cylinders are so stained. 



Histological Characters. 



Central Segments (Plate III. fig. 4). — The central segments of all three, down to 

 about 5 mm. from the seat of reunion, present the characters of a normal sciatic nerve. 

 Comparison with sections made from the opposite sciatic, brings out only one difference, 

 namely, that the nerve is thicker than the normal sciatic, and that this increase in bulk 

 is due not to any numerical increase of nerve fibres, not to any hypertrophy of the 

 fibres themselves, nor to overgrowth of connective tissue, but to the fact that the 

 individual nerve fibres are separated by wider spaces than in the normal nerve. The 

 increase in thickness is thus due to distension of the lymphatic spaces surrounding the 

 nerve fibres. At a distance of about 5 mm. from the termination of the central 

 segments, the alteration in character of the nerve commences ; for here many of the 

 medullated nerve fibres are seen to cease abruptly, often in bulbous ends, and their 

 place to be occupied by a bundle of young nerve fibres. As the termination of the 

 segment is further approached, this replacement of old fibres by new becomes more and 

 more complete, until, finally, no adult medullated fibres are present, and the entire 

 fasciculus is composed of new-formed nerve fibres. The only difference between the 

 three central segments is that of the stage of development ; for, while in Exp. I. no 

 distinct traces of degeneration products remain, in Exp. II. there are distinct remains 

 of the old myelin situated between the young nerve fibres, and the same is also the 

 case, but to a much less extent, in the central segment from Exp. III. 



Peripheral Segments (Plate III. fig. 5). — The peripheral segments of all three agree 

 in presenting full regeneration of young nerve fibres, and this is the case throughout the 

 entire nerve and its branches, muscular and cutaneous. All were examined, both close 

 to the seat of reunion and far removed from it, without showing any adult nerve fibres. 

 In Exp. I. the nerve close to the seat of reunion presents many young fibres, which are 

 well developed, each presenting a clearly defined axis-cylinder, traceable for considerable 

 distances in the section, a well-marked but thin medullated sheath, and a deli 



