176 PKACTICAL PHYSIOLOGY 



III. True Proteids. These contain hexone bases, mon-amido acids, 

 and aromatic radicles. Thsy include all the commoner proteids, and 

 may be further subdivided into four sub-groups, viz. : 



(a) Native Proteids. These give all the proteid reactions, and are 

 coagulated by heat and by the prolonged action of alcohol. There are 

 two varieties, albumins and globulins, which differ from one another 

 in solubility. 



Albumins are soluble in distilled water and in saturated solutions 

 of all neutral salts except ammonium sulphate and anhydrous sodium 

 sulphate, in which they are insoluble. They are, however, soluble in 

 half-saturated solutions of these salts. 



Globulins are insoluble in distilled water and in saturated solutions 

 of all neutral salts. They are, moreover, insoluble in half-saturated 

 solutions of ammonium sulphate and anhydrous sodium sulphate. 

 They are soluble in weak saline solutions. 



EXPERIMENT XIII. Take some blood-serum. This consists of a 

 weak saline solution containing albumin and globulin. Divide it into 

 three parts, a, b, and c. Allow' a to drop into a beaker filled with 

 distilled water; a cloud forms round each drop as it mixes with the 

 water. This is due to precipitation of the globulin, as there is 

 now too little saline to keep it in solution. (See Advanced Course.) 



Saturate b with crystals of MgS0 4 a precipitate of globulin is pro- 

 duced. Filter. The filtrate gives all the proteid reactions because it 

 contains the albumin; the precipitate can be dissolved by mixing it 

 with water, the weak saline solution thus produced dissolving the 

 globulin, which can be recognised by applying the proteid tests. 



To c add an equal bulk of a saturated solution of Am 2 S0 4 . This 

 produces half saturation in the mixture, as a result of which globulin is 

 precipitated. The precipitate and filtrate should be examined in the 

 same way as the MgS0 4 precipitate. 



The chief kinds of albumins are ovo- and serum-albumin. 



The chief kinds of globulins are ovo- and serum-globulin, myosin- 

 ogen (the chief proteid of muscle) and fibrinogen (an important proteid 

 of living blood). 



TABLE FOR SEPARATION OF ALBUMINS AND GLOBULINS. 



Solvent. Albumin. Globulin. Practical method of separation. 



a. Distilled water, - - soluble insoluble dialysis. 



b. Weak saline, - - soluble soluble 



c. Saturation with\ i w- a i KI O /Saturation with crystals of 

 MgS0 4 ,NaCl,etc.,j ' soluble insoluble | either salt. 



. .} ( Half saturation by adding an 



Half saturation with I _ goluble insoluble J equal volume of saturated 

 Am 2 S0 4 , Is a 2 S0 4 , j (^ solution of either salt. 



