CHEMIC COMPOSITION OF THE HUMAN BODY 15 



bodies, they are regarded as the simplest of all the proteins. Since a typical 

 protein always yields on hydrolysis the hexone bases, in addition to a variable 

 number of mono-amino-acids, it is believed that the usual protein is com- 

 posed of a nucleus of the hexone bases to which is attached a variable 

 number of mono-amino-acids. The proportions in which the bases exist 

 in the nucleus and the proportions in which the ammo-acids are united to 

 the nucleus, vary in different proteins. 



HISTONS. 



The proteins embraced in this class comprise a series of compounds 

 which are somewhat more complex than the protamins and less complex 

 than the typical proteins; for on hydrolysis they not only yield the hexone 

 bases but in addition a large number of mono-amino-acids. They are, there- 

 fore, intermediate in structural composition between the protamins and the 

 usual proteins. Their protein character is indicated by their reaction to 

 Millon's reagent and to Piotrowski's test. They are precipitated from 

 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 ammon'um 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. 



(b) 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, 



