202 



BARDWICKE'S SCIENCE-GOSSIP. 



reticulum is due to a regular crossing of the coils. 

 Carney also states that the chromatin of Flemming 

 is identical with nuclein (a substance which Miescher 

 discovered in 1871) ; that the filament is made up 

 of a tube, a lumen, and of contents which may 

 be organised ; and that the nucleolus is due to a 

 localisation of the filament. To the • protoplasmic 

 portion of the nucleus he applies the name of 

 "karyoplasma." Strasburger regards the nucleus as 

 made up of nucleoplasm (identical with Carnoy's 

 karyoplasma), which consists of a filament crossing 

 itself in coils in every direction, and in containing 

 nucleomicrosomata which do stain, and nucleohya- 

 loplasm which does not stain. Arnold Brass 

 considers the chromatic filament to be made up of 

 several substances, and to be the seat of meta- 

 morphoses. While Van Beneden, agreeing with 

 the researches of Flemming, differs in the termin- 

 ology he applies. In his paper on the fecundation of 



Fig. 125.— Karyokinetis. A, ordinary nucleus of a columnar epithelial 

 cell ; B, c, the same nucleus in a stage of convokuioii ; D, the wreath 

 or rosette form ; E, the aster or single star : F, a nuclear spindle 

 from Descemet's endothelium of the frog's cornea ; G, H, I, diaster ; 

 K, two daughter nuclei. 



Ascm-is mcgalocephala he gives the name of "nucleo- 

 plasm " to the substance forming both the membrane 

 and the reticulum, and conceives that each fibre of 

 the reticulum is made up of a great number of 

 minute particles, or nucleomicrosomata, which are 

 surrounded by the chromatin substance. The 

 nucleoplasm he describes as made up of an achro- 

 matic substance disposed as fine moniliform filaments 

 and of a chromatic substance which fills the meshes 

 and is imbibed by the network and the membrane. 

 The more elongated fibres he calls nuclear threads. 

 I have referred to the fact that Miescher in 1871 

 discovered nuclein as a constituent of the nucleus. 

 Since then Zacharias — in 1882 and 1883— has dis- 

 covered nnolher substance in the nucleus which he 

 has termed "plastin," a substance nearly related to 

 protoplasm. Nuclein has been isolated, and is a 

 greyish-coloured mass soluble in weak Na HO, but 

 insoluble in weak HCl. It is generally considered 

 to be an organic body containing phosphorus, but 



Gamgee* considers the analytical results so un- 

 satisfactory that he will not allow it to be considered 

 as "a definite chemical individual possessed of con- 

 stant composition." 



Karyokinesis, to which we must now turn onr 

 attention, was first described by Butschli in 1876, 

 but the term was first used by Schleicher. Biitschli 

 observed it taking place in the testicular cells of 

 Blatta gcrinanica, and in two cells of the blastoderm' 

 of Musca vomitoria. Perhaps the future will dis- 

 close to us that it is the only form of nuclear division^ 

 and that direct cell-division or karyostenosis f does 

 not exist. Karyostenosis, however, has been de- 

 scribed by Ranvier and Lavdowski as occurring in 

 epithelial and adipose tissue cells and in leucocytes ;. 

 perhaps, too, it is the manner of division in some 

 thallophyles and in the cells of the parenchyma of 

 the higher plants. The kinetic changes in nuclear 

 division are well illustrated by Fig. 125, which I have 

 taken from Klein's " Elements of Histology.'' 

 The changes take place as follows — according: 

 to Flemming. The nucleoli disappear, and 

 the chromatin of the nucleus becomes greater 

 in quantity and disposed in a complexly coiled 

 thread, which at ilength unravels to form the 

 spirem or " wreath-form." The peripheral ends 

 of the loops composing the wreath now become 

 divided and form the aster or garland ; then 

 each filament becomes divided along its length,, 

 and all the filaments become localised near 

 the equator of the nucleus forming an equatorial 

 group. The equatorial group soon begins to 

 be divided into two halves by the development 

 of a transparent divisional plate — the cell-plate 

 of Strasburger ; and each half moves towards- 

 opposite poles of the nucleus to give rise to- 

 the pithode or barrel-form — which is identical 

 with Eberth's and Maizel's creel-forrn or basket- 

 form. The barrel-form develops further and 

 becomes a double star or diaster. The process is- 

 now reversed. Each half of the diaster represents a 

 daughter nucleus, which after passing through the 

 star-form, then the wreath-form, and at last by 

 shrinkage into the coil-form, becomes a resting 

 nucleus. During the formation of the wreath-form, 

 of each daughter nucleus the cell-protoplasm begins 

 to divide, so that by the end of the completion of the 

 coil-form there results a divided cell, each division) 

 of which contains a nucleus. The whole process is- 

 rapid, and ends by the "constriction and severance 

 of the cell-protoplasm." 



For literature on this subject of karyokinesis I 

 recommend the reader Carnoy's " La Biologie 

 cellulaire," 1884; Ryder's "The Law of Nuclear 

 Displacement, and its Significance in Embryology " 

 (" Science," i. 1883); KoUiker's " Das Karyoplasma 



* " Physiological Chemistry," vol. i. p. 

 f A term proposed by Carnoy. 



