366 PROTEIN-COMPOUNDS. 



15*76^. No eggs but those of the common hen have as yet been 

 examined.* 



Origin. It is very easy to conceive that vitellin may be formed 

 from albumen or fibrin, but in the yet imperfect state of our know- 

 ledge regarding albumen and fibrin as well as vitellin, we cannot 

 chemically trace out this metamorphosis. Since, however, it is 

 poorer in carbon, and somewhat richer in oxygen, than albumen, it 

 may, like fibrin, be regarded as one of the first stages of the meta- 

 morphosis of albumen by the action of oxygen, and as a certain 

 form of non-spontaneously coagulating fibrin. 



Uses. From the position in which vitellin occurs and from its 

 analogy with other albuminous substances, it is obviously one of 

 those nutrient substances which are employed in the formation 

 of the animal tissues. We are however entirely ignorant of the 

 chemical equations representing these changes ; from the admirable 

 work of Baudrimont and Martin St. Angef we may however at 

 least draw the conclusion that this substance loses a portion of its 

 nitrogen and assimilates oxygen in its conversion into tissue. (See 

 the " History of Development " in the third volume.) 



GLOBULIN. 

 Chemical Relations. 



Properties. This body, which has also received the name of 

 crystalling occurs naturally in the soluble state, but becomes inso- 

 luble on boiling. Soluble globulin, when dried at 50, forms a 

 yellowish, transparent mass, which may be easily triturated, and 

 then yields a snow-white powder ; it is devoid of smell and taste, 

 swells like albumen in water, and gradually dissolves, forming a 

 viscid solution containing merely a few flakes ; after precipitation 

 by alcohol from this solution, it is insoluble in water, but, like 

 casein, is partially soluble in boiling alcohol ; on cooling, however, 

 it again separates from this solution. The aqueous solution of 

 globulin is coagulated by ether. When dried, the soluble modifi- 

 cation may be heated to 100 without passing into the insoluble 

 state. It is distinguished from albumen and vitellin, which are 

 very similar to it, by the following properties ; its solution does 

 not become opalescent at a lower temperature than 73 ; at 83 it 



* [Gobley has recently examined the eggs of the carp, which in their chemical 

 composition seem very similar to those of the common hen. Journ. de Chim. 

 meU T. 6, p. 67. G. E. D.] 



t Ann. de Chim. et de Phys. T. 21, pp. 195-257. 



