CHEMIC COMPOSITION OF THE HUMAN BODY. 19 



hydroxid. A blue-violet color is produced, which deepens some- 

 what on heating, but no further change ensues. 



The proteids found in the animal body, though possessing many 

 features in common, are nevertheless characterized by certain special 

 features which not only serve for their identification, but for their 

 classification into well-defined groups, as follows : 



SIMPLE PROTEIDS. 



1. ALBUMINS. 



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

 solutions, and in saturated solutions of sodium chlorid and magnesium 

 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 rotary power of 62.6. 

 (fr) 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 rotary 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 (one 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, in- 



