FATfi AXD IJI'O/ns (/.//'/ V.ST) 23 



111 tlie cell the imcleo-proteins probably exist partly as solid struc- 

 tures, c. g., the chromatin framework of the nucleus, and partly dis- 

 solved in the plasma. An interesting phenomenon is the alteration in 

 the chromatin nueleo-proteins durin<>: cell division, when they seem to 

 lose part of the combined protein 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. g., mono-, di-, and 

 tribasie ])li()sphates. in this we have a chemical explanation of the 

 intensity of the staining of dividing nuclei by basic dyes.'' 



Phosphoproteins. Of these, by an luifortunate similarity of name, 

 the so-called "nucleo-albumins" are often confused with nueleo-pro- 

 teins by non-chemical writers, a difficulty increased by an actual re- 

 semblance to the extent that they also yield phosphoric acid, and are 

 somewhat similar in solubility and digestibility. They are essentially 

 different, however, in that they do not yield nucleic acid or purine 

 bases on cleavage. Probably members of this group are also constant 

 components of cells. 



Glycoproteins (or gluco-proteins) and pliospho-glycoproteins are 

 also believed to occur frequently or constantly in protoplasm. They 

 are compounds of proteins with a sugar or sugar-like group, which 

 probably usually contains nitrogen, thus differing from the ordinaiy 

 hexoses and pentoses. 



Insoluble proteins, or bodies resembling the coagulated proteins in 

 their lack of solubility in various fluids, are left behind after the 

 other proteins have been extracted from the cells. Their signitieance 

 is not known : whether to a large extent artificially produced or 

 whether a normal structural element of the cell. 



FATS AND LIPOIDS (LIPINS) 



Lipoids is a term in common use but of indefinite significance ; most 

 usually it comprehends the intracellular substances which are soluble 

 in ordinaiy fat solvents, but which are not simple fats or fatty acids, 

 lecithin and cholesterol being the most important of the lipoids. For 

 the entire group of fats and lipoids the term lipins has been proposed 

 by Gies and Rosenbloom. Lipoids and ordinary fats, that is lipins, 

 occur in all cells, but their demonstration is not always readily pos- 

 sible. The microscopic appearance of a cell, even when special stains 

 for fat are used, gives no correct idea of the amount of lipins actually 

 present. Thus normal kidneys contain 15 to 18 per cent, in their dry 

 substance, but none of this can be detected readily with the micro- 

 scope. A kidney which seems microscopically the site of marked fatty 

 degeneration may show no more fat when examined chemically than a 

 normal kidney, which in section appears to be quite free from fat. 

 This is because some of the intracellular fat is bound chemically with 



8 The oheniistrv of the niicleo-proteins is discussed in the chapter on Frio Acid 

 Metabolism and Gout. Chap. xxi. 



