THE NATIVE ALBUMINS. 47 



IV. The albuminoids (collagen, elastin, spongin, fibroin, amyloid, 



albumoid, pigments which are derived from albumins). 

 V. The derived albumins : 



1. The coagulated albumins. 



2. The album inates. 



3. The albumoses. 



4. The peptones and protones. 



THE NATIVE ALBUMINS. 



The general physical and chemical properties of the native albu- 

 mins as a class have been described in the foregoing pages. The 

 remarks which follow apply more particularly to the various sub- 

 divisions, as follows : 



The Albumins. The albumins, in the narrower sense of the term, 

 comprise serum-albumin, egg-albumin, and lactalbumin. They are 

 soluble in water, dilute saline solution, and in dilute acids and alka- 

 lies. They are precipitated from their solutions with greater diffi- 

 culty than the globulins and many proteids. Sodium chloride and 

 magnesium sulphate cause their precipitation only if the reaction is 

 acid ; in neutral solutions no precipitation occurs. Ammonium 

 sulphate precipitates the albumins upon complete saturation ; the 

 limits of precipitation are 6.4 and 9, the reaction being neutral ; if 

 acid, they are a little lower. 



All the members of the group are coagulated by heat. 



One of the most interesting properties of the albumins is their 

 ability to crystallize. 



To hydrolytic decomposition by mineral acids and proteolytic fer- 

 ments the albumins are comparatively resistant. Notable is the 

 large amount of sulphur of serum-albumin and egg-albumin ; with 

 the exception of the keratins these bodies contain more sulphur 

 (1.6 to 2.2 per cent.) than any other proteins. The end-products of 

 hydrolysis are typical of the proteins as a class. 



The Globulins. These comprise the various globulins of the 

 blood (the serum-globulins and fibrinogen), ovoglobulin, lactoglobu- 

 lin, myosin, myogen, various cell-globulins, and vegetable globulins. 

 They are all soluble in dilute solutions of the alkalies and neutral salts, 

 while as a class they are insoluble in distilled water and dilute acids. 

 There is one notable exception, however. If a dilute saline solution 

 of the common serum-globulin of the blood-plasma, for example, is 

 subjected to dialysis, a certain portion of the globulin is precipitated 

 (euglobulin), while another portion remains in solution, and may 

 be demonstrated by saturating with magnesium sulphate or by half- 

 saturation with ammonium sulphate (pseudoglobulin). With the 

 exception mentioned, the globulins are precipitated from their solu- 

 tions by dialysis, on copious dilution with water, by acidifying with 

 a dilute mineral acid or with acetic acid, and even by passing a 

 stream of carbon dioxide through the solution. By saturation with 



