1030 APPENDIX. 



albumin, milk-albumin (lactalbumin) , and egg-albumin (ovalbumin). They 

 are characterized as a class by the fact that they are coagulable by heat in 

 solutions with a neutral or acid reaction, and are soluble in water free from 

 salts. In accordance with the latter part of this definition they are not 

 precipitated by dialysis. They are precipitated from their solutions with 

 more difficulty by saturation with neutral salts, ammonium sulphate, than 

 the globulins with which they are usually associated. Empirically, as regards 

 the liquids of the body, it is stated that they require more than half saturation 

 with ammonium sulphate for precipitation (see section on Blood). All 

 three albumins referred to here may be obtained in crystallized form. They 

 are not precipitated by saturation with sodium chlorid or magnesium sul- 



Ehate unless the solution is made acid. They are rich in sulphur, containing 

 *om 1.6 to 2.2 per cent., and on hydrolysis they yield no glycocoll. 



The Globulins. Proteins belonging to this group are found in the cell 

 tissues together with albumins. The forms that have been most studied 

 are serum-globulin (paraglobulin) and fibrinogen (blood, lymph, and transu- 

 data), milk-globulin (lactoglobulin), and egg-globulin. As contrasted with 

 the albumins, they are coagulable by heat, but are insoluble in pure water. 

 They are readily soluble in dilute solutions of neutral salts, that is, salts of 

 strong bases with strong acids. In consequence of their insolubility in water 

 they are precipitated by dialysis. This reaction is not distinctive, however, 

 as the precipitation is not coniplete. Some of the so-called globulin remains in 

 solution after the salts have been removed as completely as possible by 

 dialysis. They are also precipitated partially from their dilute solutions by 

 the addition of weak acids or by a stream of carbon dioxid. Practically they 

 are isolated from accompanying albumins by precipitation with neutral salts. 

 In neutral solutions the globulins are completely precipitated by saturation 

 with magnesium sulphate or half saturation with ammonium sulphate. In 

 the blood several different forms of globulin are distinguished by the degree 

 of saturation with ammonium sulphate necessary for their precipitation (see 

 Blood). The separations made by this method are not, however, satisfac- 

 tory. Nor, indeed, is the separation between globulins and albumins alto- 

 gether satisfactory. It would seem that these proteins are so closely related 

 that distinctive reactions are difficult to obtain on account of the existence 

 of forms intermediate between the extremes that are used as types. 



The Glutelins. These proteins occur in abundance in the seeds of 

 cereals. They are insoluble in all neutral solvents, but are readily dissolved 

 by very dilute acids or alkalies. 



Alcohol-soluble Proteins (Prolamines). Found in quantity in cereals, 

 but not in other seeds. They are soluble in alcohol (70-80 per cent.), but 

 insoluble in water or in absolute alcohol. Gliadin of wheat and rye and hor- 

 dein of barley are examples. On hydrolysis these proteins give a very large 

 percentage of glutaminic acid (20 to 37 per cent.) and from 20 to 30 per cent, 

 of their nitrogen is given off as ammonia.* 



Albuminoids. Simple proteins which are characterized by great in- 

 solubility in all neutral solvents. They form the principle constituent of 

 the skeletal tissues and connective tissues, epidermis, hairs, etc., including 

 such members as elastin, keratin, and collagen. Physiologically it has been 

 found that gelatin, a derivative of collagen, does not suffice for the construction 

 of living protein, and cannot be used in place of the other proteins to main- 

 tain nitrogen equilibrium. This peculiarity seems to be due to the absence 

 of certain necessary amino-acids in its molecule. (See p. 910.) 



Protamins and Histons. The histons are defined as being soluble in 

 water and insoluble in very dilute ammonia. They yield precipitates with 

 solutions of other proteins and give a coagulum on heating. Protamins 

 are soluble in water, not coagulated by heating, and, like the histons, have 

 the property of precipitating other proteins in aqueous solutions. They 

 possess strong basic properties and form stable salts. The protamins have 

 been obtained (Miescher-Kossel) from the heads of the spermatozoa in fishes, 

 in which they exist in combination with nucleic acid. They differ considerably 



* For description of this and other vegetable proteins, see Osborne, 

 "Science," Oct. 2, 1908. 



