CHEMICAL BASIS OF THE ANIMAL BODY. 25 



A dilute saline solution of this proteid coagulates at 75. Bechamp 

 has recorded 1 some determinations of its specific rotatory power which 

 must however be accepted with caution. 



2. Vitellin 2 . 



This constitutes the characteristic proteid constituent of egg-yolk 

 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 identical in their general properties 

 and reactions with vitellin. As obtained in conjunction with some 

 lecithin by exhaustion of egg-yolk with ether, it consists of a white, 

 pasty, granular mass, insoluble in water, readily soluble in solutions of 

 sodium chloride which may be easily filtered. Unlike other true 

 globulins it cannot be precipitated from this solution by saturation 

 with sodium chloride. Its saline solutions (10 p.c. NaCl) are co- 

 agulated by heating to 75. It is readily soluble in 1 p.c. sodium 

 carbonate, is incompletely 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, vitellin is associated in egg-yolk with 

 lecithin and (?) nuclein. It has not as yet been obtained free from 

 admixture with the former, and a theory has been advanced 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 extraction with ether in a Soxhlet or other 

 form of apparatus. 



Fr6my 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 sufficiently investigated. 



The primary products obtained from vitellin by the digestive action 

 of pepsin have been examined and described by Neumeister 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 of 8 10 

 p.c. sodium chloride solution, precipitated from this by the addition 



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



2 Dumas et Cahours, Ann. Chem. et Phys. (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. xii. (1876), S. 635. Zt. f. physiol. Chem. 

 Bd. i. (1877), S. 72. 



3 Compt. Rend. T. xxxvni. pp. 469, 525, 570. 



4 Zt. f. Biol. Bd. xxm. (1887), S. 402. Cf. Chittenden and Hartwell, Jl. of Physiol. 

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



