26 INTRODUCTION 



stains. In the cytoplasm, on the other hand, the nucleo-proteids 

 have the acid quite saturated with proteids and hence are devoid 

 of acid properties, which is also indicated by their lack of 

 affinity for hematoxylin and other basic dyes. The term nucleic 

 acid also covers a large group of substances, which are charac- 

 terized, on the one hand, by their frequent occurrence bound with 

 proteids, and, on the other hand, by their yielding phosphoric 

 acid and purin bases, pyrimidins and pentoses on cleavage. 

 Diagram matically the manner of cleavage of the nucleo-proteids 

 may be indicated as follows : 



Nucleoproteid 



nuclein l proteid 

 nucleic acid proteid 

 phosphoric acid purin bases, pyrimidins and pentoses. 



The enormous variety of nucleo-proteids that may possibly 

 exist can be imagined when we consider that there exist several 

 different sorts of purin bases, not all of which are found in 

 any one nucleic acid, that the form of phosphoric acid present 

 may vary, that the proteids are of different varieties, that the 

 proportions of each ingredient is perhaps never twice the same, 

 and furthermore that many nucleo-proteids contain carbohydrate 

 groups. The possible combinations of these ingredients is little 

 short of infinite and it may well be that we have here a partial 

 explanation of the innumerable varieties of living organisms. 2 



In the cell the nucleo-proteids probably exist partly as solid 

 structures, e. g., the chromatin framework of the nucleus, and 

 partly dissolved in the plasma. An interesting phenomenon is 

 the alteration in the chromatin nucleo-proteids during cell 

 division, when they seem to lose part of the combined proteid 

 and approach more nearly pure nucleic acid -just as inorganic 

 salts occur with the acids and bases saturating each other more 

 or less incompletely, e. <r/., mono-, di-, and tribasic phosphates. 

 In this we have a chemical explanation of the intensity of the 

 staining of dividing nuclei by basic dyes. 



Nucleo-proteids combined with carbohydrates, nucleo-gluco- 

 proteids, are probably important and perhaps constant cell con- 

 stituents. It is of interest to note that the carbohydrate is 

 often not one of the ordinary hexoses, such as glucose, but one 

 of the more uncommon pentoses. 



1 Probably nuclein should be considered as merely one variety of nucleo- 

 proteid, with less proteid than the other varieties. 



2 The chemistry of the nucleo-proteids is also discussed in the chapter on 

 Uric Acid Metabolism and Gout, Chap. XXI. 



