716 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Division of Leucocytes.* * * § — Prof. W. Flemming recognizes, as others 
have recognized, that free, colourless, amoeboid cells, with polymorphic 
nuclei, in short with the characteristics of leucocytes, occur as wandering 
cells in the connective tissue and as inhabitants of the medullary spaces, 
and that they multiply abundantly by mitosis. It is certain that leuco- 
cytes divide both with and without mitosis. Like so many other cells 
they exhibit attraction-spheres and central corpuscles, but these do not 
seem to be implicated in the fragmentation or direct division of the 
nucleus. As to the significance of the two modes of division, Flemming 
comes to the following important conclusions : — The leucocytes multiply 
by mitosis, only the products of mitotic division live on and multiply ; 
fragmentation of the nucleus, with or without division of the cell, lias 
not to do with the production of new cells, but is a degeneration or an 
aberration ; in some cases, where multinuclear cells are formed, it 
perhaps influences cellular metabolism by increasing the nuclear 
surface. 
Structure of Striped Muscle.t — Dr. J. B. Haycraft finds that an 
“ impression ” of a muscle-fibre on a film of collodion shows in every 
detail the appearances characteristic of the muscle used to stamp it, in 
whatever state of contraction or relaxation that muscle may be. This 
confirms Dr. Haycraft in his previous conclusions as to the structure of 
striped muscle, for as the stripings are well seen on the films, they must 
be in part due to varicosities of the fibrils. The interfibrillar substance 
is of the nature of a matrix perforated by varicose tubes. There are two 
chief varieties of fully differentiated muscular tissue : — (a) There is the 
nucleated spindle devoid of sarcolemma and made up of fibrils cemented 
together, and these spindles may be striped or unstriped, the difference 
depending upon the rapidity of their contraction. (6) There is a second 
type consisting of cylindrical threads, sometimes invested by a sarco- 
lemma, and with nuclei within the fibrils, under the sarcolemma, or in 
both of these situations, and these threads of tissue are striped or un- 
striped, according to the rapidity of their contraction. Striated muscle 
is defined as “ muscular tissues, the ultimate fibrils of which have be- 
come varicose, in association with the power of quicker and more active 
movement.” When a fibril segments into a number of much smaller 
portions, each one contracting and relaxing on its own account, tho 
contractions are necessarily more rapid. 
Prof. A. Rollett J insists on the reality of the accessory disc ( Neben - 
scheiben) or N-stripe of striated muscle-fibres. Retzius has recently 
maintained that this is merely due to a regular row of sarcoplasmic 
granules. Rollett maintains that it is due to definite anisotropic 
segments of the fibrils. This is shown by the appearance in polarized 
light, in alcoholic maceration, in stained preparations, as well as by the 
behaviour of the N-stripe during the contraction of the fibre. 
Structure of Nerve-cells. § — Sig. G. Magini would make the fol- 
lowing additions to the differential characters of nerve-cells. The 
* Archiv f. Mikr. Anat., xxxvii. (1891) pp. 249-98 (2 pis.). 
t Proc. Roy. Poc. Lond., xlix. (1891) pp. 287-303 (1 pi. and 5 figs.). 
j Archiv f. Mikr. Anat., xxxvii. (1891) pp. 654-84 (1 pi.). 
§ Atti R. Accad. Lincei— Rend., vi. (1890) pp. 19-23; vii. (1891) pp. 277-9. 
