CHAPTER III. 



THE NUCLEOPROTEINS, NUCLEINS AND 

 NUCLEIC ACIDS. 



Nucleic acid is a complicated organic acid containing 

 phosphorus, which is found widely distributed in animal 

 and vegetable tissues. It is a special constituent of the 

 nuclei and is therefore most abundant in cellular organs, 

 such as the thymus, the pancreas, the testis, and the 

 lymphatic glands. 



Nucleic acid forms salt-like combinations, with proteins, 

 the amount and nature of the protein combining with the 

 nucleic acid varying considerably. Such combinations are 

 known as nucleo-proteins . They are soluble in water and 

 dilute salt solutions. They show acidic properties, being 

 soluble in alkalies and precipitated by dilute acids. They 

 dissolve to form an opalescent solution in excess of strong 

 acetic acid. (Distinction from mucin.) 



A rather special form of nucleoprotein is nucleohistone , 

 in which the nucleic acid is combined with the basic protein, 

 histone. It has similar physical properties to those of the 

 other nucleoproteins, but is precipitated as a calcium com- 

 pound by 0-2 per cent, calcium chloride solution. 



On digesting nucleoprotein with pepsin and hydro- 

 chloric acid, the greater part of the protein is removed as 

 peptone, but a certain amount is still left combined with 

 the nucleic acid. This compound is known as nuclein. It 

 is insoluble in water and dilute salt solutions, but is soluble 

 in dilute alkalies. 



By hydrolysis of nuclein by pancreatic juice or better by 

 dilute alkalies, the remainder of the protein is removed, 

 and there is obtained nucleic acid. 



Nucleic acid is not hydrolysed by trypsin, but it is 



