26 PROTEIDS. 



of an excess of water, and purified by resolution in the salt and 

 reprecipitation by the addition of water. The operations must be 

 conducted as rapidly as possible since the prolonged action of water 

 renders the vitellin insoluble in saline solutions. If any attempt is 

 made to separate the vitellin from lecithin residues by means of 

 alcohol it is at once converted into ordinary coagulated proteid. 



3. Paraglobulin. (Serum-globulin 1 .} 



This proteid occurs most characteristically in blood-serum (also in 

 lymph), in amounts now known to be much larger than was at one 

 time supposed, and thus constituting about one-half of the total 

 proteids of the serum 2 . 



Preparation*. The older methods consisted in (1) diluting serum 

 ten-fold with water and passing a prolonged current of carbonic acid 

 gas; (2) saturating serum with sodium chloride. The amount of 

 precipitate thus obtained represents only a small part of the total 

 paraglobulin present in the serum 4 , and the only satisfactory method 

 of preparing it pure and in considerable quantity is as follows : 

 (3) serum is saturated at 30 with magnesium sulphate, by means of 

 which paraglobulin is quantitatively precipitated. The precipitate 

 collected by nitration is distributed through a small volume of a 

 saturated solution of the magnesium salt, collected on a filter and 

 washed with saturated solution of MgSO 4 . By this means it is 

 separated from the larger part of the serum-albumin. 



To effect its final and complete separation from this latter proteid, 

 two methods may be Adopted, (a) The precipitate is dissolved in 

 water, then largely diluted and the paraglobulin further separated 

 out by passing a stream of C0 2 . (j8) The precipitate is dissolved as 

 before in water, the paraglobulin again salted out by MgSO 4 , this 

 process repeated several times, and the final product separated from the 

 magnesium salt by dialysis 5 . 



1 This is the substance to which Al. Schmidt gave the name of fibrino-plastin 

 (Arch. f. Anat. u. Physiol. Jahrg. 1861, Sn. 545, 675. Ibid. 1862, Sn. 428, 533. 

 Pfliiger's Arch. Bd. vi. (1872), S. 413. Ibid. xi. (1875), Sn. 291, 526.) _ It had 

 previously been described under the name ' serum- casein ' by Panum. (Virchow's 

 Arch. Bd. iv. (1852), S. 17). The name paraglobulin is due to Kuhne (Lehrbuch 

 1868, Sn. 168, 175.) It is now generally and most appropriately known by the 

 latter name, or that of serum-globulin, as suggested by Hoppe-Seyler. 



2 Hammarsten, Pfliiger's Arch. Bd. xvn. (1878), S. 413. Salvioli, Arch. f. 

 Physiol. 1881, S. 269. 



3 Gamgee, Physiol. Chem. Vol. i. p. 37. 



4 Hammarsten, loc. cit. Heynsius, Pfliiger's Arch. Bd. xn. (1876), S. 549. 



5 Hammarsten, loc. cit. Also Pfliiger's Arch. Bd. xvm. (1878), S. 38. Zt. f. 

 physiol. Chem. Bd. vin. (1883), S. 467. Denis had previously used magnesium 

 sulphate for the quantitative separation of serum-globulins (" M^moire sur le Sang, 

 1859"), but Hammarsten rediscovered the general method independently, and 

 applied it somewhat differently to Denis. On the use of ammonium sulphate for 



