32 TEXT-BOOK OF PHYSIOLOGY. 



bones, where they constitute 20 per cent, and 30 per cent, respectively. 

 Though genetically related, and possessing many features in common, 

 the different members of the proteid group are distinguished by 

 characteristic physical and chemic properties which serve not only 

 for their identification, but for their classification into more or less 

 well-defined groups as follows: 



1. NATIVE PROTEIDS. 



The members of this group are soluble in water, in dilute saline 

 solutions, and in saturated solutions of sodium chlorid and mag- 

 nesium sulphate. They are coagulated by heat, and when dried 

 form an amber-colored mass. 



(a) Serum-albumin is found in blood, lymph, chyle, tissue 

 fluids, and milk. It is obtained readily by precipitation from 

 blood-serum, after the other proteids have been removed, on 

 the addition of ammonium sulphate. When freed from saline 

 constituents, it presents itself as a pale, amorphous substance, 

 soluble in water and in strong nitric acid. It is coagulated 

 at a temperature of 73 C., as well as by various acids e. g., 

 citric, picric, nitric, etc. It has a rotatory power of 62.6. 

 (6) Egg-albumin. Though not a constituent of the human 

 body, egg-albumin resembles the foregoing in many respects. 

 When obtained in the solid form from the white of the egg, 

 it is a yellow mass without taste or odor. Though similar 

 to serum-albumin, it differs from it in being precipitated by 

 ether, in coagulating at 54 C., and in having a lower rotatory 

 power, 35.5.' 



2. GLOBULINS. 



The members of this group are insoluble in water and in saturated 

 solutions of sodium chlorid and magnesium sulphate and ammonium 

 sulphate. They are soluble, however, in dilute saline solutions 

 e. g., sodium chlorid (i per cent.), potassium chlorid, ammonium 

 chlorid, etc. They are coagulated by heat. 



(a) Serum-globulin or Paraglobulin. This proteid, as its name 



implies, is found in blood-serum, though it is present in other 

 animal fluids. When precipitated by magnesium sulphate 

 or carbon dioxid, it presents itself as a flocculent substance, 

 insoluble in water, soluble in dilute acids and alkalies, and 

 coagulating at 75 C. 



(b) Fibrinogen. This proteid is found in blood-plasma in asso- 



ciation with serum-globulin and serum-albumin. It is also 

 present in lymph-tissue fluids and in pathologic transudates. 

 It can be obtained from blood-plasma which has been pre- 

 viously treated with magnesium sulphate on the addition of 



