PROTEIDS OF PLASMA. 163 



Albumins of Hood plasma. The albumins of plasma are also found 

 in the serum after coagulation of blood, and hence they^ have been 

 termed serum albumins. They remain in plasma or serum after half- 

 saturating it with ammonium sulphate, i.e. by mixing it with an equal 

 amount of saturated ammonium sulphate solution, or after entirely 

 saturating it with magnesium sulphate. 



The precipitated globulins and nucleo-proteid are removed by filtra- 

 tion, and the filtrate dialysed to remove the salts. The solution which 

 remains contains only the albumins ; they can be precipitated from it by 

 saturation with ammonium sulphate or by sodio-magnesium sulphate. 

 According to Giirber, they can be obtained in a crystalline form by 

 adding ammonium sulphate just sufficient to produce precipitation and 

 allowing the fluid to stand exposed to the air. 1 



The material obtained in these ways constitutes what has usually 

 been called serum albumin (serine), but, as Halliburton has shown, 2 it is 

 really a mixture of three separate albumins, which he has termed 

 respectively a, ft, y. These differ from one another in their temperature 

 of heat coagulation ; a-albumin coagulates at 72 75 C. ; /3-albumin at 

 77-78 C. ; and -/-albumin at 83-86 C. In the plasma of horse, ox, 

 and sheep blood, a-albumin is absent, but the other two are present ; in 

 man, and all other mammals and birds investigated by Halliburton, all 

 three were present ; but in reptiles, amphibia, and fishes investigated, 

 a-albumin was usually the only one found. 3 



The crystals of serum albumin which were obtained by Giirber from the 

 serum of horse's blood were hexagonal prisms with one pyramidal end, 

 and were doubly refracting ; some of them were as much as 1 cm. long. 

 Their elementary composition was C, 53'1 ; H, 7'1 ; N, 15'9 / S, 1-9, 

 0'22 ; and ash, O22 per cent. Dissolved in water and the excess of 

 ammonium sulphate removed by dialysis, the solution had a heat coagulation 

 temperature of 51 to 53, and a specific rotation for yellow light of -6 1 . 4 



The globulins of blood plasma. The globulins of blood plasma con- 

 sist of serum globulin and fibrinogen. Serum globulin (paraglobulin, 

 Kiihne ; fibrino-plastic substance, A. Schmidt) has a heat coagulation 

 temperature of 75 C., which is almost constant in all animals in 

 which it has been examined. The amount to which it is contained 

 in plasma is represented by the figures in the second column of the 

 table on p. 162. It will be seen from this, that in man it constitutes about 

 three parts per cent, of the total serum. It is precipitated from serum by 

 half-saturation with ammonium sulphate, 5 and also by complete saturation 

 with magnesium sulphate, sodium chloride, and some other neutral salts 

 which do not precipitate the albumins ; also, but less completely, by dilut- 

 ing the serum with water (fifteen times) and passing C0 2 through it, or by 



1 Sitzungsb. d. phys.-med. Gesellsch. zu Wilrzburg, 1894, S. 143. 



2 Journ. PkysioL, Cambridge and London, vol. v. p. 152. 



3 In the slider terrapin (Howell, John Hopkins Univ. Stud. biol. lab., Baltimore, vol. 

 iii. p. 49) the albumin present is apparently of the variety, coagulating at 77 to 80, 

 and in the eel and dog-fish this variety was also found by Halliburton (Journ. PhysioL, 

 Cambridge and London, vol. vii. p. 320). 



4 Michel (with Giirber), Verhandl. d. phys.-med. Gesellsch. zu Wiirzlmrg, 1895, N". F., 

 Bd. xxix. No. 3. 



5 Kauder (Arch. f. exper. Path. u. Pharmakol., Leipzig, 1886, Bd. xx. S. 411) found 

 that solutions of ammonium sulphate stronger than 24 per cent, completely precipitated 

 serum globulin ; above 33 '5 per cent, some of the serum albumin also comes down. A 

 half-saturated solution contains about 26 per cent. 



