108 PROTEIDS. 



coagulated proteid. Some proteids are precipitated by certain 

 reagents, and not by others, and this fact is made use of to dis- 

 tinguish the proteids from one another. 



The following table gives the temperature at which the differ- 

 ent albumins coagulate : 



Albumins. Temperature. 



Serum-albumin 



a) 73 C. 



0) ' 77 



7) 



78 



Egg-albumin 



Lactalbumin 77 



Myo-albumin 73 



Serum-albumin. The fluid of blood in its normal condi- 

 tion is plasma; after coagulation, serum. The albumin of blood 

 remains in the serum after blood has coagulated, and hence is 

 known as serum-albumin. When to plasma or serum is added an 

 equal amount of a saturated solution of ammonium sulphate, the 

 fluid is said to be half saturated with ammonium sulphate. In 

 this condition the globulins and nucleoproteids are precipitated, 

 but not the albumin. The same result is obtained by completely 

 saturating it with magnesium sulphate. If now the fluid is filtered, 

 the globulins and nucleoproteids will be filtered out, and the fil- 

 trate (the liquid which has passed through the filter) may be put 

 into a dialyzer, and the salts will thus be removed, leaving only 

 the serum-albumin. The fact that exposure of serum-albumin to 

 different temperatures (about 73 C., 77 C., and 84 C.) results, 

 in three separate coagulations indicates that what is called serum- 

 albumin is in reality three different substances or forms, which are 

 called respectively a-albumin, which coagulates at 72 to 75 C. ; 

 /9-albumin, coagulating at 77 to 78 C. ; and y-albumin, coagulating 

 at 83 to 86 C. Halliburton, to whom we owe this information, has 

 ascertained that in the plasma of the horse, ox, and sheep a-albumin 

 is absent, while /9-albumin and y-albumin are present ; in the rep- 

 tiles, amphibians, and fishes, the blood of which he examined, only 

 a-albumin was normally found, while in that of man and of all 

 other mammals and birds all three were present. 



Magnesium sulphate does not precipitate serum-albumin, while 

 it does serum-globulin, so that by this reagent the two may be 

 separated, the salt being added in crystals until the solution is 

 completely saturated ; or, as stated, half-saturation with ammo- 

 nium sulphate will bring about the same result. 



The specific rotatory power of solutions of serum-albumin is 

 -56. 



1gg- albumin. As its name implies, egg-albumin is obtained 

 from the white of egg. If much of it is taken in the food, or if 

 it is injected into the blood, part of it appears in the urine. 

 When shaken with ether it is precipitated. Nitric acid, heat, and 



