22 \•KTERlI\AR^' PATHOLOGY. 



plasm varies in different cells and even in diiTerent parts ol 

 the same cell. Particles of food and various other insoluble sub- 

 stances are not uncommon in the cell body. \'acuoles are fre- 

 (juentlv observed, especially in wandering cells. 



The nucleus is constant in all functioning- or active cells except 

 the mammalian red blood corpuscles, and some of the pulmonary 

 alveolar epithelial cells. The nucleus appears as a dense body 

 and is usuallv centrallv located in the cell body. The relative 

 proportion of nucleus to cell body is inconstant, e. -g., the 

 lymphocyte is practically all nucleus; some epithelial cells have 

 a ver^- small nucleus and a ver-^- large cell body. The nucleus 

 varies in shape from a sphere to an irregular mass, and is sur- 

 rounded bv an incomplete membrane. The essential structure 

 of the nucleus is a chromatin network. The spongioplasm 

 and hyaloplasm of the cell bodv are continuous through the 

 incomplete nuclear membrane into the nucleus \\diere they are 

 designated linin and nucleoplasm respectively. The nucleus mav 

 also contain a nucleolus which is probablv a knot in the chro- 

 matin network. 



The centrosome is a dense refractile body found in the 

 nucleus or in the cell bod}^ just outside the nuclear membrane. 

 Manv fine radiating fibres may extend outward from the centro- 

 some. 



A cell membrane mav or mav not be present. This mem- 

 brane is formed by a condensation of the substance of the cell 

 body. The sarcolemma of a muscle fibre is perhaps the most 

 t)'pical cell membrane found in animal cells, the red corpuscle 

 has a modified cell membrane. A nerve cell possesses a neuri- 

 lemma, although it is probabU- not a true cell membrane. 



Shape.^Embryonic cells are usually spherical in shape and 

 it is probable that sphericity is a primitive cjuality of cells. The 

 shape of matured cells is determined bv their function and loca- 

 tion. External surface cells are usually flat and when subject 

 to pressure and friction thev are arranged in strata, i. e., thev 

 are stratified. The cells lining the air vesicles are flat because 

 of the necessity of the exchange of gases through them. Muscle 

 cells are elongated to allow of contraction to produce motion. 

 Goblet cells are large and more or less spherical because of the 

 elaboration of mucus in them. Accommodation to space pro- 

 duces variation in the shape of cells, thus ; fat cells are originally 

 spherical, but because of pressure, thev become polyhedral. Cells 

 vary from the flat pavemental cells to those spherical in shape. 



Pressure is probably the most important factor in the produc- 



