I.] THE PROTEIDS. 5 



varies considerably with a large number of conditions. When 

 dried at 40 C. they yield a clear yellow coloured mass, " soluble 

 albumin," which is soluble in water. 



(i.) Egg- Albumin. Prepare a solution (Lesson I. 1.). 



(a. ) Evaporate some of the fluid to dryness at 40 C. over a water-bath to 

 obtain "soluble albumin." Study its characters, notably its solubility in 

 water. This solution gives all the tests of egg-albumin. It is more con- 

 venient to purchase this substance. 



(6.) The fluid gives all the general proteid reactions. 



(c.) Precipitate portions of the fluid with strong mineral acids, 

 including sulphuric and hydrochloric acids. 



(d.) Precipitate other portions by each of the following : Mer- 

 curic chloride, basic lead acetate, tannic acid, alcohol, picric acid. 



(e.) Take 5 cc. of the fluid, add twice its volume of o.i per cent, 

 sulphuric acid, and then add ether. Shake briskly = coagulation 

 after a time, at the line of junction of the fluids. 



(/.) The solution is not precipitated on saturation with crystals 

 of sodic chloride or magnesic sulphate, but it is completely pre- 

 cipitated on saturation with ammonium sulphate (NH 4 ) 2 80 4 (com- 

 pare " Globulins "). 



(.'/.) A solution containing 1-3 per cent, of salts coagulates at 

 about 56 C. 



(2.) Serum-Albumin. Blood-serum (see "Blood") contains 

 serum-albumin and serum-globulin. Dilute blood-serum until it 

 has the same specific gravity as the egg-albumin solution. A slight 

 opalescence, due to precipitation of serum-globulin, is obtained. 

 Neutralise- the solution with very dilute acid until a faint haziness 

 is obtained. 



Eepeat the tests for egg-albumin, and, in addition, with undiluted 

 blood-serum. 



(h.) Add crystals of MgS0 4 to saturation, shaking the flask 

 vigorously to do so = a white precipitate of serum-globulin. Filter. 

 The nitrate contains serum-albumin. 



(i.) Saturate serum with (NH 4 ) 2 S0 4 = white precipitate of both 

 serum-albumin and serum-globulin. Filter. The filtrate contains 

 no proteids. 



EGG-ALBUMIN. SERUM-ALBUMIN. 



(i.) Eeadily precipitated by (i.) It is also precipitated by 



hydrochloric acid, but the pre- hydrochloric acid, but not so 



cipitate is not readily soluble in readily, while the precipitate is 



excess. soluble in excess. 



(ii.) A non-alkaline solution (ii.) It is not coagulated by 



is coagulated by ether. ether. 



