PHYSIOLOGY OF THE CELL. 31 



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

 in the protoplasm, is a small body, the centrosome, or pole corpuscle. 



Chemic Composition of the Cell. The composition of living pro- 

 toplasm 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 protoplasm is the seat of constructive and 

 destructive processes, 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 protoplasm is a highly complex compound the 

 resultant of the intimate union of many different substances. About 

 seventy-five per cent, of protoplasm consists of water and twenty-five 

 per cent, of solids, of which the more important compounds are 

 various nucleo-proteids (characterized by their large percentage of 

 phosphorus), globulins, traces of lecithin, cholesterin, and frequently 

 fat and carbohydrates. Inorganic salts, especially the potassium, 

 sodium, and calcium chlorids and phosphates, are almost invariable 

 and essential constituents. 



MANIFESTATIONS OF CELL LIFE. 



Growth, Nutrition. All cells exhibit the three fundamental prop- 

 erties of life viz., growth, nutrition, reproduction. All cells when 

 newly reproduced are extremely small, but by the absorption of nutri- 

 tive material from their surrounding medium, they gradually grow 

 until they attain their mature size. This is accomplished by the 

 power which living material possesses of transforming, vitalizing, 

 and organizing crude nutritive material, through a series of upward 

 changes, into material similar to itself. To all these changes the 

 term assimilation, or anabolism, has been given. Some of the ab- 

 sorbed material, in all probability, never becomes an integral part 



