CHEMICAL RELATIONS OF NUCLEUS AND CYTOPLASM 239 



a sponge-like network. Cell-organs, such as the nucleus, the spindle 

 and asters, the centrosome, are to be regarded as specialized areas 

 in this network, just as the visible organs of the multicellular body 

 are specialized regions in the all-pervading cellular tissue. And pre- 

 cisely as the various organs and tissues are the seat of special chemi- 

 cal activities leading to the formation and characteristic transformation 

 of specific substances, as for instance haemoglobin is characteristic 

 of the red blood-corpuscles, or chlorophyll of the assimilating tissues of 

 plants, so in the cell the various morphological regions are areas 

 of specific chemical activities and are characterized by the presence 

 of corresponding substances. The morphological differentiation of 

 cell-organs is therefore in a way the visible expression of underlying 

 chemical specializations ; and these are in the last analysis reducible 

 to differences of metabolic action. 



i. The Proteids and their Allies 



The most important chemical compounds found in the cell are the 

 group of protein substances; and there is every reason to believe that 

 these form the principal basis of living protoplasm in all of its forms. 

 These substances are complex compounds of carbon, hydrogen, nitro- 

 gen, and oxygen, often containing a small percentage of sulphur, and 

 in some cases also phosphorus and iron. They form a very exten- 

 sive group of which the different members differ considerably in 

 physical and chemical properties, though all have certain common 

 traits and are closely related. They are variously classified even by 

 the latest writers. Halliburton ('93) employs the word " proteids " 

 as synonymous with albuminous substances, including under them the 

 various forms of albumin (egg-albumin, cell-albumin, muscle-albumin, 

 vegetable-albumins), globulin (fibrinogen, vitellin, etc.), and the pep- 

 tones (diffusible hydrated proteids). This author places in a sepa- 

 rate class of albuminoids another series of nearly related substances 

 (reckoned by some -chemists among the " proteids "), examples of 

 which are gelatine, mucin, and especially nuclein, and the nucleo- 

 albumijis. The three last-named bodies are characterized by the 

 presence of phosphorus, in which respect they show a very definite 

 contrast to the " proteids," many of which, such as egg-albumin, con- 

 tain no phosphorus, and others only a trace. By Hammarsten and 

 some others the word "proteid" is, however, employed in a more 

 restricted sense, being applied to substances such as the nucleins 

 and nucleo-proteids, of greater complexity than the albumins and 

 globulins. The latter, together with the nucleo-albumins, are classed 

 as albuminous bodies (Eiweisskorper). 1 



1 See Hammersten, '95, p. 1 6. 



