TEXT-BOOK OF PHYSIOLOGY. 



completely incloses the cell substance. The cell membrane is permeable 

 to water and watery solutions of various inorganic and organic substances. 

 It is, however, not an essential part of the cell. 



The nucleus is a small vesicular body embedded in the cytoplasm near 

 the center of the cell. In the resting condition of the cell it consists of a 

 distinct membrane, composed of amphipyrenin, inclosing the nuclear con- 

 tents. The latter consists of a homogeneous amorphous substance the 

 nuclear matrix in which is embedded the nuclear network. It can often 

 be seen that a portion of one side of the nucleus, called the pole, is free from 

 this network. The main cords of the network are arranged as V-shaped 

 loops about it. These main cords send out secondary branches or twigs, 

 which, uniting with one another, complete the network. The nuclear cords 

 are composed of granules of chromatin so called because of its affinity for 



Nuclear membrane. % 



Linin. 



Nuclear fluid (matrix). - ./ 



Nucleolus. 



Chromatin-cords ,,. 

 (nuclear network). 



Nodal enlargements ^-'' 

 of the chromatin. 



Cell membrane. 

 Exoplasm. 



Microsomes. 

 Centrosoma. 



' ~ Spongioplasm. 

 ']/ Hyaloplasm. 



Foreign inclosures. 



FIG. i. DIAGRAM OF A CELL. Microsomes and spongioplasm are only partly drawn. (Stohr.) 



certain staining materials held together by an achromatin substance 

 known as linin. Besides the nuclear network, there are embedded in the 

 nuclear matrix one or more small bodies composed of -pyrenin, known as 

 nudeoli. At the pole of the nucleus, either within or just without in the 

 cytoplasm, is a small body, the centrosome, or pole corpuscle. 



Chemic Composition of the Cell. The composition of living bioplasm 

 is difficult of determination, for the reason that all chemic and physical 

 methods employed for its analysis destroy its vitality, and the products 

 obtained are peculiar to dead rather than to living matter. Moreover, as 

 bioplasm is the seat of extensive chemic changes, it is not easy to determine 

 whether the products of analysis are crude food constituents or cleavage or 

 disintegration products. Nevertheless, chemic investigations have shown 

 that even in the living condition bioplasm is a highly complex compound 

 the resultant of the intimate union of many different substances. About 

 75 per cent, of bioplasm consists of water and 25 per cent, of solids, of 

 which the more important compounds are various nucleo-proteins (char- 

 acterized by their large percentage of phosphorus), globulins, lipoids, such 

 as lecithin (a phosphorized fat) and cholesterin (a monatomic alcohol) and 



