22 THE CHEMISTRY AXD PHYi^ICS OF THE CELL 



Globulins also occur in all cells, but in small amounts in most ani- 

 mal cells except the muscles, whose chief proteins belong to this or a 

 closelj' related group. The globulins are quite similar to the albu- 

 mins, so that there is really no sharp line between the two groups. 

 Their insolubility in water separates them from albumins, and their 

 solubility in dilute neutral salt solutions from the more complex pro- 

 teins. An important feature of the globulins is the low tempera- 

 ture at which they coagulate — some so low that Halliburton ^ believes 

 it possible that they may be coagulated within the cells during high 

 fevers. 



Hammarsten has long maintained that simple proteins form a 

 relatively insignificant part of the cytoplasm, in opposition to the 

 once-prevalent view that the nucleo-proteins were limited to the 

 micleus, and that the cytoplasm was chiefly albumin and globulin. 

 The general trend of opinion as influenced by the results of researches 

 has been favorable to his contentions, and we shall probably not be far 

 wrong in accepting his statement that — ''The chief mass of the pro- 

 tein substances of the cells does not consist of proteins in the ordinary 

 sense, but consists of more complex phosphorized bodies, and that the 

 globulins and albumins are to be considered as nutritive materials for 

 the cells or as destructive products in the chemical transformation of 

 the protoplasm. ' ' ^ 



Nucleo-proteins are probably the most important constituents of the 

 cell, both in quantity and in relation to cell activity. In structure 

 the nucleo-proteins are very complex, as indicated by the different 

 products yielded on hydrolytie cleavage of the molecule. Further- 

 more, there are many varieties, depending both upon the nature and 

 proportions of the component parts. They may be described as con- 

 sisting of two primarj^ constituents — (1) nucleic acid and (2) a pro- 

 tein body, in chemical combination with each other like a salt. The 

 term nucleic acid covers a large group of substances, which are 

 characterized, on the one hand, by their frequent occurrence bound 

 with proteins, and, on the other hand, by their yielding phosphoric 

 acid and purine bases, pyrimidines and pentoses or hexoses on cleav- 

 age. Diagrammatically the manner of cleavage of the nucleo-proteins 

 may be indicated as follows: 



Niicleo-protoin 



nuclcin 7 protein 



/\ 



nucleic acid ])rotcin 



/\ 



phosphoric a<'i(l ])minc bases, jiyrimidines ajid carltohydrates. ^ 



5 Hallilmrton and ISfott, Archives of Ncurolopy. 100.3 (2). 727; also see TTalli- 

 biirton's "Chemistry of Muscle and Nerve." 



<i See Kossel, Miincli. nied. Woch.. 1011 (.')8), fi.''). 



7 Proltahly nncleiii should he considered as merely one variety of niicleoin'otein, 

 with less protein llian the other varieties. 



