NUCLEI. 33 



more particles, like minute granules, called nudem- 

 corpuscles, or nucleoli (fig. 1, c). Other nuclei, again, appear 

 to be formed simply of a small mass of protoplasm. 



The composition of the nucleus is uncertain. One of its 

 most general characters, and the most useful in micro- 

 scopic examinations, is, that it is neither dissolved nor 

 made transparent by acetic acid, but acquires, when that 

 fluid is in contact with it, a darker and more distinct outline. 

 It is commonly, too, the part of the mature cell which is 

 capable of being stained by an ammoniacal solution of 

 carmine the test, it may be remarked, by which, 

 according to Dr. Beale, protoplasm or germinal matter 

 may be always known. 



Nuclei may be either free or attached. Free nuclei are 

 such as either float in fluid, like those in some of the 

 secretions, which appear to be derived from the secreting 

 cells of the glands, or lie loosely imbedded in solid 

 substance, as in the grey matter of the brain and spinal 

 cord, and most abundantly in some quickly- growing 

 tumours. 



Attached nuclei are either closely imbedded in homo- 

 geneous pellucid substance, as in rudimental cellular tissue ; 

 or are fixed on the surface of fibres, as on those of 

 organic muscle- and organic nerve-fibres ; or are enclosed 

 in cells, or in tissues formed by the extension or junction 

 of cells. Nuclei enclosed in cells appear to be attached to 

 the inner surface of the cell- wall, projecting into the cavity. 

 Their position in relation to the centre or axis of the cell 

 is uncertain ; often when the cell lies on a flat or broad 

 surface, they appear central, as in blood-corpuscles, 

 epithelium- cells, whether tesselated or cylindrical; but, 

 perhaps, more often their position has no regular relation 

 to the centre of the cell. In most instances, each cell 

 contains only a single nucleus ; but in cartilage, especially 

 when it is growing or ossifying, two or more nuclei in 

 each cell are common ; and the development of new cells 



D 



