64 NUCLEOPROTEINS, NUCLEINS, NUCLEIC ACIDS. [CH. III. 



A heavy precipitate of nucleoprotein and nucleohistone is formed. 

 Allow this to settle in a cylinder : pour or pipette off as much of the 

 supernatant fluid as possible, and filter the remainder. Note that 

 the precipitate is soluble in dilute alkalies and is reprecipitated by 

 acidification ; that it dissolves to an opalescent solution in excess of 

 acetic acid (difference from mucin) ; and that it gives all the usual 

 colour reactions of proteins. 



74. To another portion add one-tenth of its volume of 2 per 

 cent, calcium chloride and warm to 37 C. A white precipitate of 

 nucleohistone is formed. Pour off the supernatant fluid, and to this 

 fluid add dilute acetic acid drop by drop; a white precipitate of 

 nucleoprotein is produced. 



75. Precipitate the nucleoprotein and nucleohistone from the 

 remainder of the fluid by means of acetic acid as in Ex. 73. Collect 

 the precipitate on a filter paper, allow it to drain well, and then 

 transfer it by means of a spatula to a small thimble-shaped porcelain 

 capsule. Heat carefully, first to drive off the water, and then to 

 carbonise the residue. Add one-third of a crucible full of fusion 

 mixture (K 2 CO 3 two parts, KNO 3 one part), and heat as strongly as 

 possible till the mass fuses. Allow the melt to cool, and extract it 

 with nitric acid (diluted with an equal quantity of distilled water) 

 till the mixture no longer effervesces. Filter: treat the filtrate 

 with about one-tenth of its volume of strong nitric acid and one- 

 third its volume of ammonium molybdate ; boil for two minutes. 

 A yellow precipitate of ammonium phospho-molybdate separates 

 out, often on the sides of the vessel. The phosphorus of the nucleic 

 acid has been oxidised to phosphoric acid. 



76. Preparation of thymus nucleic acid. (After W. Jones.) 

 To a boiling mixture of 2 litres of water, 100 grms. sodium acetate and 

 23 grms. of caustic soda, add in small successive portions I kilo, of 

 trimmed and finely ground calves thymus. Immerse the vessel for 

 two hours in boiling water, stirring occasionally. Dilute with one- 

 third volume of water and make faintly but distinctly acid to litmus 

 with 50 per cent, acetic acid. The amount of acid required is 

 usually about 100 cc., but the final additions must be made extremely 

 cautiously until a point is reached which allows of good filtration. 



