PHYSIOLOGY OF THE CELL. 43 



of pyrenin, known as nucleoli. At the pole of the nucleus, either 

 within or just without in the protoplasm, is a small body, the centro- 

 some, or pole corpuscle. 



Chemic Composition of the Cell. The composition of living 

 protoplasm 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. 

 ^Abojat^5_r^cent. of protoplasm ^cpjisislS-ol .water and. .25..; per cent. 

 ol solids, i of which the more important compounds are various 

 nucleo-proteids (characterized by their large percentage of phos- 

 phorus), globulins, traces ojjecithin, cholesterin, and freqp^ptJy fat 

 and carbohydrates^ Inorganic saltsp^spmstliy 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 



properties of life viz., growth, nutrition, reproduction. All cells 

 when newly reproduced are extremely small, but by the absorption 

 of nutritive 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 

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

 of the living bioplasm, but undergoes disruption and oxidation, 

 giving rise at once to heat and force. Coincident with the assimila- 

 tive processes, a series of disintegrative processes is constantly taking 

 place, whereby the living material is reduced, through a series of 

 downward chemic changes, to simpler compounds, such as water, 

 carbon dioxid, urea, etc. To all these downward changes the term 

 dissimilation, or katabolism, has been given. As a result, also, of 

 these various changes, the protoplasm gives rise to the production 

 of material of an entirely different character, such as globules of fat, 

 granules of glycogen, mucigen, digestive ferments, etc. The sum 

 total of all changes which go on in the cell, both assimilative and 

 dissimilative, are embraced under the general term nutrition, or 



