132 JOHN PRIESTLEY. 



upon nuclei, their nature, microchemical reactions, and 

 growth. 



Nuclei in a perfectly recent and normal state, are de- 

 scribed as flexible and elastic vesicles with a somewhat 

 thick, highly refractile, doubly contoured membrane which 

 appears to be less distinctly separated from the cell proto- 

 plasm than from the interior of the nucleus. This membrane 

 is regarded as having been formed about the original drop- 

 like nucleus by the differentiation of the inmost layer of 

 protoplasm into a species of interior cell membrane. The 

 main body of the nucleus is bright, and is called by 

 Auerbach the ground substance. It includes one or more nu- 

 cleolijSmooth bodies of irregular outline, as well as numbers of 

 extremely fine iiitermediary granules. These are either 

 impartially scattered throughout the nucleus, or arranged 

 so as to leave a clear zone about the nucleoli, and sometimes 

 also a similar zone beneath the nuclear membrane (Plate XI, 

 fig. 1, a— d). 



When nuclei liberated from the cell-body were submitted 

 to the action of certain reagents, characteristic changes of 

 appearance occurred. Water, added gradually, by irrigation, 

 to nuclei so prepared causes, as a first effect, a shrinking, 

 associated with the expression of droplets of a hyaline body 

 which is supposed to exist in the interstices of the nuclear 

 ground substance. These droplets cling to the irregular cir- 

 cumference of the nucleus and fill the hollows due to shrink- 

 ing (Plate XI, fig. 1, e — g, m). The intermediary granules 

 swell up and most of them become invisible ; the interior of 

 the nucleus assumes a darker, shining, almost homogeneous 

 appearance, the distinction of wall and contents becoming 

 less marked; while the nucleoli at this stage are very 

 slightly affected. 



If irrigation with water be continued the nucleolus 

 begins to swell up, filling the whole of the nucleus and 

 fusing with the membranous wall (Plate XI, fig. 1, 1). If 

 several nucleoli coexist in the same nucleus they may present 

 different degrees of resistance to the action of the water. In 

 the mean time the nucleus has attained to its original size ; 

 but continued exposure soon results in increased dimensions. 

 When this point has been reached, the nucleus successfully 

 resists any further destructive action of the water, not, as 

 is generally thought, becoming completely disintegrated. 

 Some of the later steps in the above process may be retraced 

 by treating the nucleus with a 1 per cent, solution of NaCl, 

 when nucleoli and the nuclear wall become again visible, 

 showing that no true solution has occurred. 



