!' PKOTEIDS. 



Bdchamp has recorded l some determinations of its specific rota- 

 tory power which must however be accepted with caution. 



2. Vitellin. 2 



This constitutes the characteristic proteid constituent of egg- 

 volk and is also largely present in caviar Some at least of the 

 globulins present in vegetable protoplasm, and more particularly 

 in the crystals of the aleurone grains, appear to be identic-ill in 

 their genera J properties and reactions with vitellin. As obtained 

 in conjunction with some lecithin by exhaustion of egg-yolk witli 

 ether, it consists of a white, pasty, granular mass, insoluble^ in 

 water, readily soluble jiLsolutions of sodium chlojride which may 

 be easily filterecT Unlike other true globulins it cannot be pre- 

 cipitated from this solution by saturation with sodium_chloride. 

 Its saline solutions (lu p.c. NaCl^ are coagulated by heating to 

 2$. It is readily soluble in 1 p.c. sodium carbonate, is incom- 

 pletely precipitated from this solution by dilution with water, 

 but fairly completely by the additional passing of a stream of 

 carbonic acid gas through the diluted solution. 



As has been already stated, vitej.lin_Js associated in egg-yolk 

 with lecjthin and (?) njiclein. It has not as yet been obtained 

 free from admixture with the former, and a theory has been ad- 

 vanced that it is really a complex substance resembling in this 

 respect haemoglobin, which on treatment with alcohol splits up 

 into coagulated proteid and lecithin. It is possible that pure 

 vitellin free from lecithin might be obtained by prolonged ex- 

 traction with ether in a tjoxhlet or other form of apparatus. 



Fre"my and Valenciennes have described 3 a series of proteids, viz. 

 ichthin, ichthidin &c. derived from the eggs of fishes and amphibia. 

 They appear to be closely related to vitellin but have not been suffi- 

 ciently investigated. 



The primary products obtained from vitellin by the digestive 

 action of pepsin have been examined and described by Neu- 

 meister. 4 



Preparation. Egg-yolk is extracted with successive portions 

 of ether as long as the residue yields any colour to the solvent. 

 The pasty residue thus obtained is dissolved in a minimal amount 



1 Compt. Rend. T. xc. (1880), p. 1255. 



2 Dumas et Cahours, Ann. Chem. e.t Phi/s. (3) T. vi. p. 422. Hoppe-Seyler, Med.- 

 chem. Unters. (Tubingen), Hft. 2 (1867), S! 215. Weyl, Arch. f. Physiol. Jahrg. 1876, 

 S. 546. Pfliiger's Arch. Bd. xn. (1876), S. 635. Zt. f. phys'fot. Chem. Bd. i. (1877), 

 S. 72. 



8 Compt. Rend. T. xxxvin. pp. 469, 525, 570. 



4 Zt. f. Biol. Bd. xxin. (1887), S. 402. Cf. Chitteuden and Hartwell, .//. of 

 Physiol. Vol. xi. (1890), p. 441. 



