CHEMIC COMPOSITION OF THE HUMAN BODY 15 



neutral solution by alkaloid reagents. The histons are usually found 

 in combination with nucleic acid, in the spermatozoa of most animals and 

 especially in fish, and in the coloring matter (the hemoglobin) of the red 

 corpuscles. The proteins of the tissues usually contain from 25 to 30 per 

 cent, of histons. 



ALBUMINS. 



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

 tions, 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. This most important protein is found in blood, 

 lymph, chyle, and some tissue fluids. It is obtained readily by 

 precipitation from blood-serum, after the other proteins have been 

 removed, on the addition of ammonium sulphate. When freed 

 from saline constituents, it presents itself as a pale, amorphous sub- 

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

 at a temperature of 73C., 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 54C., and in 

 having a lower rotatory power, 35.5. 



(c) Lact-albumin. As its name implies, this protein is found in milk. 

 It can be precipitated from milk-plasma by sodium sulphate after 

 the precipitation of the other proteids by half saturation with am- 

 monium sulphate. It slowly coagulates at 77C. 



(d) Myo-albumin. This protein is found in muscle-plasma from 

 which it subjects the plasma to fractional heat coagulation. At 

 73C. myo-albumin coagulates. 



GLOBULINS. 



(a) Serum-globulin or Paraglobulin. This protein, 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 75C. 



(b) Fibrinogen. This protein is found in blood-plasma in association 

 with serum-globulin and serum-albumin. It is also present in 

 lymph-tissue fluids and in pathologic transudates. It can be ob- 

 tained from blood-plasma which has been previously ^ treated with 

 magnesium sulphate on the addition of a saturated solution of sodium 

 chlorid. It is soluble in dilute acids and alkalies, and coagulates 

 at 56C. 



(c) Paramyosinogen or Myosin. This protein is a constituent of the 

 muscle-plasma from which it can be precipitated by a temperature 



of 47C. 



(d) Myosinogen or Myogen. This protein is the chief constituent of 

 the muscle-plasma and is of great nutritive value. During the 

 living condition it is liquid, but after death it readily undergoes a 



