NOTES AND MEMORANDA. 



Studies of the Microscopic Images of Mt dullated Nerve Fibre. 

 By Professor Franz Boll (' Reale Accadeniia dei Lincei 

 Roma,' June 4th, 18T6.)— The author of this impor- 

 tant paper commences by referring to the researches of 

 Zawerthal, Schmidt, and Lantermann, who independently 

 published in 1874 descriptions of the discontinuity of the 

 medullary sheath. The first named, however, confuses the 

 medullary sheath with the sheath of Schwann, to which 

 latter he refers the discontinuity which really belongs to the 

 former; the second considers the appearance of discontinuity 

 to be produced by folds of the medullary sheath, and to be 

 of slight importance; only Lantermann, in his preliminary 

 publication (' Centralblatt,' 1874, p. 106), has accurately 

 recognised and described the discontinuity in question. Boll 

 first recognised this particularity of structure independently, 

 in the autumn of 1875, in the electric nerves of the torpedo 

 and continued to study the subject further, using exclusively 

 the sciatic nerve of adult Rana esculanta. His descriptions 

 of this and other points are as follows : — 



A. — Nerve Fibre m Salt Solutioji, '75 %. 



When examined in this ** physiological " fluid, the medul- 

 lary sheath appears to be constituted of separate medullary 

 segments, of which there are from twenty to thirty in each 

 nerve-segment {i.e. part of the nerve comprised between two 

 Ranvier's nodes). The dimension of these medullary seo-- 

 ments varies, the shortest being often not longer than the 

 transverse diameter of the nerve-fibre, while others are from 

 twelve to fifteen times that length. Each of these segments 

 is tubular, surrounding the axis-cylinder, and they fit into 

 each other by their free ends. One segment may thus 

 embrace, or be embraced by another, or it may embrace at 

 one extremity and be embraced at the other. This latter 

 is the usual arrangement, and the segments then appear 

 imbricated, like tiles on a roof. It also rarely happens that 

 a medullary segment, instead of ending in a sharp edge, as is 

 the rule, terminates by a channelled margin (appearing bi- 



