THE CELL DOCTRINE. 109 



A circumscribed round or oval portion of germinal 

 matter within the cell is usually termed the nucleus, 

 which may be surrounded by formed material as in 

 the superficial epithelial cell, or by other germinal 

 matter as in the white blood corpuscle. 



In the nutrition of the cell, the pabulum comes 

 to it from the periphery; being strained through the 

 formed material, and the new germinal matter takes 

 its place in or near the centre of the original mass, 

 constituting a new centre of germinal matter, which 

 may be the nucleus, if no other circumscribed centre 

 be present, or the nucleolus if it be deposited within 

 such a centre. Other new centres may again take 

 position within these, and assume the relation ol 

 nucleolus to the original nucleolus, which now be- 

 comes the nucleus, an older centre of germinal mat- 

 ter; while the original nucleus has probably been 

 converted into the second constituent of the cell, the 

 formed material. 



Germinal matter when free and living, exhibits a 

 power of movement, both in portions of its substance, 

 producing changes in shape, and in its entire mass, 

 resulting in changes of position. The former, and 

 probably, also, the latter, may have for their object 

 the obtaining of pabulum, as is seen in the amoeba, 

 when it embraces by its protrusions, a particle of nu- 

 tritive matter. These movements are less decided in 

 the cells of the higher animals, yet they are of con- 

 stant occurrence, as in pus and white corpuscles, and 

 when thus occurring they are spoken of as " amoeboid 

 movements." Allied or identical with this second 

 class of movements, are those of undoubted occur- 



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