306 PKACTICAL PHYSIOLOGY 



solutions of ammonium sulphate and anhydrous sodium sulphate. 

 They are soluble in weak saline solutions (see table, p. 312). 



The chief kinds of albumins are egg albumin, serum albumin (see 

 Blood), and lactalbumin (see Milk). 



The most important globulins are egg globulin, serum globulin, 

 fibrinogen (for both see Blood), and myosinogen (see Muscle). 



THE PHOSPHOPROTEINS. 



The chief members of this group are the caseinogens of milk and 

 the vitellins from egg-yolk. They derive their name from the large 

 amount of phosphorus contained in their molecule. They differ, how- 

 ever, from nucleoproteins in containing no purin bases. 



Dissolve some commercial caseinogen in 2 % caustic soda, and perform 

 the following EXPERIMENTS : 



(I.) Note that it is precipitated with 1 % acetic acid, the precipitate 



being soluble in excess of acid. 



(II.) Perform the colour tests for protein, and record your results. 

 (III.) Perform the " salting out " tests with Am 2 SO 4 and MgS0 4 . 

 (IV.) Heat the solution. 



With the solid substance perform the following experiments : 

 (V.) Heat some solid caseinogen upon a piece of broken porcelain 

 with " combustion mixture " (a mixture of sodium carbonate 

 and potassium nitrate). When cool, extract with nitric acid, 

 filter, add ammonium molybdate in nitric acid, and heat. 

 The canary yellow precipitate denotes phosphates. 

 (VI.) Heat a little caseinogen with 1 % NaOH in the incubator or 

 on a water bath at 37 C. for twenty -four hours. Phosphoric 

 acid is broken off. Precipitate the phosphoric acid, after 

 acidifying with acetic acid and filtering, by the addition of 

 ammoniacal magnesium citrate. Filter. Dissolve the pre- 

 cipitate in nitric acid, and test with molybdate as above. 

 (VII.) Make a solution of caseinogen in lime water. Show that it 

 is clotted by rennet. 



In connection with the above experiments it will be found that case- 

 inogen yields all the colour tests except Molisch. It therefore contains 

 no carbohydrate group (see p. 279). The xanthoproteic, Millon's, and 

 the glyoxylic tests will be very well marked, showing that caseinogen 

 is rich in tyrosin and tryptophane. 



In "salting out" caseinogen behaves like a globulin, being pre- 



