lyo BIOLOGICAL LECTURES. 



only method known to me which does so satisfactorily is the 

 excellent safranine-gentian violet-iodine stain of Hermann (pub- 

 lished in 1889 in the Arch. f. mikr. A^iatomie), by which the 

 resting chromatin is colored violet, and the dividing chromatin 

 a bright red. By the term " dividing chromatin " is understood 

 the chromatin from about the commencement of the prophasic 

 loose spirem stage until about the commencement of the ana- 

 phase. This method of Hermann cannot be too highly rec- 

 ommended for cytological work, and in many respects is far 

 superior to the favorite method of the day, the iron haematox- 

 ylin stain, with which it is difficult to secure satisfactory differ- 

 entiation of the various cell constituents. 



To return to our first spermatocyte, at the stage of the last 

 spermatogonic metakinesis. The fourteen short chromosomes 

 are stained red until the nuclear membrane appears; they 

 seem to be all alike in form and color. At the commence- 

 ment of the anaphase the chromosomes become irregular in 

 outline and elongated, and now lose the red and commence to 

 take on the violet stain, passing first through a purple stage. 

 But now a most remarkable phenomenon is to be noted : one 

 of the fourteen chromosomes does not become violet but re- 

 mains red, the color characteristic for the dividing chromatin. 

 As the anaphase proceeds, thirteen chromosomes gradually 

 become intensely violet, while the fourteenth remains red. 

 The latter is the " chromatin nucleolus," as it has been 

 termed by me ; genetically it is a chromosome, but destined to 

 have an entirely different metamorphosis from the others. The 

 chromosomes and the chromatin nucleolus continue to elon- 

 gate until their length nearly equals that of the diameter of 

 the nucleus. Then the chromatin nucleolus ceases to elongate, 

 passes to the periphery of the nucleus, and gradually shortens 

 up into a more or less spherical form ; during this process it 

 may divide into two or three parts, in which case one is usually 

 much larger than the others. At this time the true nucleolus, 

 which does not stain at all, or only a faint lilac, is forming at 

 the periphery of the nucleus ; it may at every stage be sharply 

 distinguished from the chromatin nucleolus. The thirteen true 

 chromosomes elongate to a length of about double the diameter 



