I.] THE PROTEIDS. 7 



(e ) Saturate blood-serum with crystals of sodium chloride or 

 neutral ammonium sulphate = separation of serum-globulin, which 

 floats on the surface. 



(/.) Precipitate the serum-globulin with magnesium sulphate, 

 and filter. To the filtrate add sodium sulphate in excess, which 

 gives a further precipitate. The filtrate may still give the reactions 

 for proteids. 



(2.) Fibrinogen, see " Blood." 



(3.) Myosin, see " Muscle." 



(4.) Vitellin.— Shake the yolk of an egg with water and ether, as long as 

 the washings show a yellow colour. Dissolve the residue in a minimal 

 amount of 10 per cent, sodium chloride solution. Pour it into a large quan- 

 tity of water, slightly acidulated with acetic acid = white precipitate of 

 impure vitellin. 



{a. ) Dissolve some of the precipitate in a very weak saline solution, and 

 observe that it is not reprecipitated by saturation with sodic chloride. 



{b.) Test some of the weak saline solution = coagulation about 75" C. 



(c.) The precipitate is readily soluble in .1 per cent, hydrochloric acid, and 

 also in weak alkalies. 



(5.) Crystallin is obtained from the crystalline lens. 



(6. ) Globin the proteid constituent of haemoglobin. 



7. III. Derived Albumins (Albuminates) are compounds of 

 proteids with mineral substances. Those produced by the action 

 of acids or alkalies on albumins and globuHns, yield respectively 

 acid-albumin and alkaU-albumin. They are insoluble in pure water 

 and in solutions of sodium chloride, but readily soluble in dilute 

 hydrochloric acid and dilute alkaUes. The solutions are not coagu- 

 lated by heat. 



(i.) Alkali-Albumin or Alkali- Albuminate. 



{a.) To dilute egg-albumin add a few drops of o.i per cent, 

 caustic soda, and keep it at 40° C. for 5-10 minutes = alkali- 

 albumin. Boil the fluid ; it does not coagulate. 



(6.) Test the reaction ; it is alkaline to litmus paper. 

 .(c.) Cool some of the alkali-albumin, colour it with Htmus 

 solution, and neutralise carefully with o. i per cent, sulphuric acid = a 

 precipitate on neutralisation, which is soluble in excess of the acid, 

 or of alkali. 



{(l.) Repeat (c); but, before neutralising, add a few drops of 

 sodium phosphate solution (10 per cent.), and note that the 

 alkaline phosphates prevent the precipitation on neutralisation, 

 until at least sufficient acid is added to convert the basic phosphate 

 into acid phosphate. The solution must be decidedly acid before a 

 precipitate is obtained. 



(e.) Precipitate by saturating it with crystals of common salt or 

 magnesium sulphate. 



(/.) Lieberkiihn's Jelly is a strong solution of alkaH-albmnin. 



