J03 ; /; : ;| ;/;: : : ^T PROTEIN SUBSTANCES. 



Synopsis of the Most Important Properties of the Different Groups of 



Albuminous Bodies. 



As it is not possible to base the classification of the different proteid 

 groups according to their constitution, we are obliged to make use of 

 their different solubilities and precipitation properties in their general 

 characterization. As there exist no sharp differences between the various 

 groups in this regard it is impossible to draw a sharp line between them. 



Albumins. These bodies are soluble in water and are not precipitated 

 by the addition of a little acid or alkali. They are precipitated by the 

 addition of large quantities ' of mineral acids or metallic salts. Their 

 solution in water coagulates on boiling in the presence of neutral salts, 

 but a weak saline solution does not. If NaCl or MgSO 4 is added to satur- 

 ation to a neutral solution in water at the normal temperature or at 30 C. 

 no precipitate is formed/ but if acetic acid is added to this saturated 

 solution the albumins readily separate. When ammonium sulphate 

 is added to one-half saturation the albumin solutions are not precipitated 

 at ordinary temperatures. Of all the native proteids the albumins 

 are the richest in sulpnur, containing from 1.6 per cent to 2.2 per cent. 

 ,So far as they have been investigated they do not yield any glycocoll 

 on acid hydrolysis. 



Globulins. These substances are, as a rule, insoluble in water, but 

 dissolve in dilute neutral salt solutions. The globulins are precipitated 

 unchanged from these solutions by sufficient dilution with water, and 

 on heating they coagulate. The globulins dissolve in water on the addi- 

 tion of very little acid or alkali, and on neutralizing the solvent they 

 precipitate again. The solution in a minimum amount of alkali is pre- 

 cipitated by carbon dioxide, but the precipitate may be redissolved by 

 an excess of the precipitant. The neutral solutions of the globulins 

 containing salts are partly or completely precipitated on saturation with 

 NaCl or MgSO 4 in substance at normal temperatures, depending upon 

 the kind of^ globulin. The globulins are completely precipitated by 

 half-saturating with ammonium sulphate. The globulins contain an 

 average amount of sulphur generally not below 1 per cent. As a differ- 

 ence between the albumins and globulins the latter yield glycocoll among 

 the hydrolytic cleavage products. 



According to J. STARKE l the globulins are not soluble in dilute salt solutions, 

 but form alkali proteid compounds whose solubility in salts is brought about by 



1 Zeitschr. f. Biologic, 40 and 42. In regard to the various views on this subject 

 see Wolff and Smits, ibid., 41; Osborne, 1. c. Hammarsten, Ergebnisse der Physiologic, 

 . Jahrg. I, Abt. 1. 



