24 PHYSIOLOGY CHAP. 



inasmuch as they contain no xanthine or purine bases, which are 

 characteristic of nucleoproteins. They differ from nucleoproteins 

 also in that the phosphorus is completely removed, as inorganic 

 phosphoric acid, by treatment with 1 per cent caustic soda at 37 C. 

 for 24 hours (Plimmer and Scott). The phosphoproteins have the 

 properties of acids; they turn blue litmus paper red, and are 

 soluble in distilled water only in the form of their alkaline salts, 

 from which solutions they can be precipitated by the addition of 

 stronger acids. Solutions of their salts do not coagulate with 

 heat. 



Histones, on the contrary, have the character of weak bases, 

 their solutions being precipitated by alkalies. 



The protamines form a very definite group, differentiated in 

 not a few particulars from the rest of the proteins : they do not 

 contain sulphur, and are richer in nitrogen and poorer in carbon 

 than the other proteins. They are distinctly basic in character, 

 more so than the histones. They have been isolated from the 

 spermatozoa of many fishes (salmine, clupine, scombrine, sturine, 

 etc.). 



We shall deal with the derivatives of the proteins, more 

 particularly with the proteoses and peptones, which result from the 

 action of the proteolytic ferments on the more complex proteins, 

 in the chapter on Digestion. 



The conjugated proteins are combinations of a protein with 

 a chemical aggregate, which is not a protein, and which Hoppe- 

 Seyler termed a " prosthetic group." In the nucleoproteins dis- 

 covered by Miescher and Bloss (1871) in cell-nuclei, this prosthetic 

 group is represented by nucleic acid: nucleoprotein therefore 

 results from a combination of protein and nucleic acid. The 

 nucleic acids are organic acids which contain phosphorus and 

 nitrogen, but no sulphur, their chemical constitution being un- 

 known. Their decomposition products, on the contrary, are known 

 to us : these are phosphoric acid, purine bases (adenine, guanine, 

 hypoxanthine, and xanthine), pyrimidine bases (thymine, uracil, 

 cytosine), pentoses (laevulinic acid). 



Of the various proteins which are able to unite with the nucleic 

 acids to form nucleoprotein, the protamines and histones are the 

 principal. These enter into the molecules of the nucleoproteins of 

 fishes' testicles. Nucleic acid is also combined with histone in 

 the leucocytes of the thymus and the nucleated red corpuscles. 



Nucleoproteins have distinct acid properties : they are soluble 

 in water and in saline solutions, still more in alkaline fluids ; 

 they are precipitated on the addition of acids, but are redissolved 

 by excess of mineral acid. 



Haemoglobin (to which we shall return in discussing Blood) 

 results from the combination of a histone (globin) and a complex 

 chemical aggregate containing iron (haematin). 



