SPECIAL METHODS. 193 



thread composed of globules or disks arranged in series 

 (chromatin-globules), which first falls into segments, each of 

 which is then split lengthwise. The half-segments thus 

 produced then separate so that one of each pair goes to 

 each daughter-nucleus. The achromatic figure consists, on 

 the other hand, of a number of very delicate threads which 

 are usually arranged in the form of a spindle, so that they 

 are called the nuclear spindle (cf. Fig. 36). 



341. The chromatic figure has, as the name indicates, a 

 high staining capacity, and is also usually much more deeply 

 stained than the nuclear framework of the resting nucleus. 

 It agrees more with the nucleoli in its behavior with stain- 

 ing media, although it does not in any case originate from 

 them. 



In most cases, a very deep staining of the chromatic 

 nuclear figure is obtained by fixing with the concentrated 

 Flemming's chrom-osmic-acetic acid mixture (cf. 309) and 

 staining with aniline-water-safranin ( 320). In consequence 

 of their deeper staining, the dividing nuclei are easily dis- 

 tinguished from the resting nuclei, even with pretty low- 

 powers. Besides the above, chromic-acid-platinum-chloride 

 ( 312) and chrom-formic acid ( 307) are especially useful 

 for fixing, and Gram's method ( 321) and the fuchsin-picric- 

 acid method ( 325), for staining the chromatic figure. In 

 most cases very good preparations of the karyokinetic fig- 

 ures are obtained by fixing with alcohol ( 300) or alcoholic 

 corrosive sublimate ( 310) or picric acid ( 303) and staining 

 according to one of the methods mentioned, or with one of 

 the numerous haematoxylin ( 314317) or carmine solu- 

 tions (31 8, 319). 



I will remark here that often the karyokinetic figures may 

 be made clearly visible without previous fixing by placing 

 sections of living tissues directly in a concentrated aqueous 

 solution of chloral hydrate, in which usually only the nucleus 

 is left, of all the cell-contents, and the chromatic figures 

 of dividing nuclei come out with especial sharpness. In 

 this way I have obtained very instructive preparations from 

 young fern-fronds. 



