826 



SCIENCE 



[N. S. Vol. XL. No. 1040' 



this stage the two daughter cells are connected 

 with one another only by a narrow bridge of 

 cytoplasm. Injury to the one causes the ap- 

 pearance of filaments in the nuclei of both. 

 The changes in the nucleus of the cell directly 

 injured take place more rapidly than do those 

 in the nucleus of the other cell. 



The formation or coming into evidence of 

 the filaments is always accompanied by a slight 

 increase in the size of the nucleus. After the 

 filaments are formed the nucleus decreases in 

 size often to something less than its original 

 size. 



The filamentous structure can be easily de- 

 stroyed. For example, on sucking the entire 

 nucleus containing filaments and nucleoli into 

 a capillary pipette the bore of which is many 

 times smaller than the diameter of the nu- 

 cleus and on blowing it out again the nucleus 

 presents itself as a homogeneous, glutinous 

 mass with no structural elements whatever. 



Frequently one comes across a cell the me- 

 chanical stimulation of which causes the ap- 

 pearance in the nucleus of ill-defined granular 

 condensations which rapidly resolve themselves 

 into the early prophase chromosomes familiar 

 to investigators in fixed material, viz., crosses, 

 rings and double Vs. The ragged outlines 

 characteristic of this stage are very pronounced 

 and are due to the irregular granular aspect 

 of the chromosomes. Gradually as one watches 

 them the chromosomes become more and more 

 compact. This appears to be due to an in- 

 crease in the number of the granules and their 

 coalescence. The large slender rings have thus 

 been observed to transform themselves into 

 ringlike, compact and homogeneous metaphase 

 chromosomes. The crosses also become com- 

 pact without losing their cross-like appear- 

 ance. The same is true of the double V. 

 One of these was observed which shortened 

 and became so compact as to appear like a 

 tetrahedron of which two opposite sides were 

 somewhat more deeply dug out than the others. 



This artificially induced formation of the 

 chromosomes is unaccompanied by the dis- 

 solution of the nuclear membrane. The 

 chromosomes soon clump together and become 

 indistinguishable in an irregular glutinous 



mass. They are extremely viscous and adhere 

 to the needle when touched. If one of the 

 early prophase chromosomes with ragged 

 granular outlines be seized by the needle and 

 rapidly pulled across the field so as to stretch 

 it the granules disappear and the whole sub- 

 stance becomes homogeneous. The entire nu- 

 clear substance is very glutinous and the 

 chromosomes can not be taken out of the nu- 

 clexis entirely free of the medium in which 

 they lie. When torn out of the cell, however, 

 in Einger's fluid, the nuclear substance very 

 soon absorbs water, swells and gradually dis- 

 appears. The chromosomes thus laid bare in 

 their turn swell and go into solution. 



The chromosomes in metaphase are plainly 

 visible. Movements while in the equator have 

 been observed, these arc ameboid, consisting in 

 a swelling of one part of the chromosomes at 

 the expense of another. One arm of a cross, 

 for instance, will swell until the cross shape 

 is indistinguishable and in another few sec- 

 onds the swelling will decrease, the chromo- 

 somes returning to their original shape. I 

 was unable to observe actual splitting of the 

 chromosomes, but anaphase figures passing 

 into telophase were frequently observed. The 

 chromosomes collect at the poles of the spindle. 

 They then swell into vesicles which appear to 

 merge into each other much as fluid droplets, 

 except that here incomplete outlines of the 

 vesicles persist for a time giving the telophase 

 nucleus an ill-defined network appearance. 



During metaphase and anaphase the chro- 

 mosomes lie imbedded in a hyaline substance 

 the viscosity of which is higher than that of 

 the surrounding cytoplasm, much resembling 

 the matrix of the resting nucleus. This kino- 

 plasmic mass retains its shape for a time after 

 the cytoplasm has been destroyed by tearing 

 and it is this that gives the characteristic 

 spindle shape of the metaphase and hour-glass 

 shape of the late anaphase figures. 



When once the chromosomes have separated 

 in metaphase, no interference short of total 

 destruction of the cell will prevent the passage 

 of the daughter chromosomes to their respec- 

 tive poles. By piercing and tearing the cyto- 

 plasm in the equator of the anaphase figure. 



