182 THE CELL DOCTRINE, 



filled with a tenacious fluid mass possessing no dis- 

 tinct wall. Each droplet then acquires a membrane 

 by dift'erentiation of the inmost layer of cell proto- 

 plasm and nuclei, and intermediary granules after- 

 wards make their appearance. Once differentiated, 

 the nuclear membrane is an integral part of the nu- 

 cleus, constituting the latter a true vesicle, isolable 

 as a whole by mechanical means.* 



The Nucleolus. — Very commonly also, though not 

 invariably attending it, a second differentiated mass 

 of matter is found within the nucleus, to which the 

 term nucleolus is applied. According to Beale, it is 

 possessed of like endowments, and is supposed to be 

 the most recently formed bioplasm, the non-vitalized 

 circulating albumen of the blood being converted 

 through the agency of pre-existing bioplasm into 

 the latter substance. If the cell normally develop, 

 the nucleolus growing becomes the nucleus, the lat- 

 ter being gradually oxidized upon its exterior and 

 converted into the cell-contents and cell-wall, while 

 a j'ounger centre of germinal matter takes the place 

 of the original nucleolus. This living matter exhibits 

 the important property of being stained by weak so- 

 lutions of various coloring matters, as carmine, anilin, 

 etc., the younger matter taking on the deeper stain, 

 and by these means its demonstration is rendered 

 strikingly easy. In rapidly growing cells, a still 

 younger centre of bioplasm may sometimes be demon- 

 strated within the nucleolus, while the nucleus re- 

 mains a distinctly differentiated mass capable of also 



* Auerbach, Organologisohe Studien, Breslau, 1878-4. 



