i8 



CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES 



The hyaloplasm is more fluid, less refractile, and stains with great diffi- 

 culty. It fills the interspaces of the spongioplasm. In this material may 

 be embedded such substances as the metaplasts mentioned above. 



The hyaloplasm contains in solution the various nutritive constituents 

 brought to the cell as well as the soluble end products of its chemical activity. 

 Here, too, are found the various hormones, oxidases and enzymes which 

 play so important a part in the cellular reactions in the different types of cells. 



Structure of the Nucleus. The nucleus when in a condition of rest 

 is bounded by a distinct membrane, the nuclear membrane, possibly derived 

 from the spongioplasm of the cell, which encloses the nuclear contents, nucleo- 

 plasm or karyoplasm. The membrane consists of an inner, or chromatic, 

 and of an outer, or achromatic layer, so called from their reaction to stains. 

 The nucleoplasm is made up of a reticular network, or chromoplasm, whose 

 interspaces are filled by the karyolymph, or nuclear matrix, a homogeneous 

 substance which is rich in proteins, has but slight affinity for stains, and is 

 supposed to be fluid in consistency. 



Cell membrane. 



Metaplasmic gran- < --'* 

 ules. 



Karyosome or net- '--'< 



knob. 



Hyaloplasm. 



Spongioplasm. 



Linin network. 

 Nucleoplasm. 



. Attraction sphere. 



Centrosome. 



., Plastids. 



'-.C\ - - \--^,-~- V- .- ----- Chromatin . 



--:--r--.?V --"->-> Nuclear membrane. 



- Nucleolus. 

 \----s-~~jf--. __ Vacuole. 



FIG. 12. Diagram of a Typical Cell. (Bailey.) 



The network is composed of linin or achromatin, a transparent unstain- 

 able framework, and of chromatin, which stains deeply. It is supported by 

 the linin, and occurs sometimes in the form of granules, but usually as irreg- 

 ular anastomosing threads, both thicker primary fibers and thinner connect- 

 ing branches. The threads often form thickened nodes, karyosomes or 

 false nucleoli, at their points of intersection. It is now quite generally be- 

 lieved that the chromatin occurs as short, rod-like, and highly refractive 

 masses, which are embedded in the linin in a regular series. 



The nucleoli, or plasmosomes, are spherical bodies which stain deeply, and 

 may either lie free in the nuclear matrix or be attached to the threads of 

 the network. 



