APR] CHEMICAL BASIS OF THE ANIMAL BODY. 713 



respect, for the solution may be easily filtered. Its coagulation tempera- 

 ture is higher than that of myosin, lying according to Weyl 1 , between 

 70 C. and 80 C. Saturation with solid sodic chloride gives no precipi- 

 tate ; in this respect it differs from most other members of this class. 

 In yolk of egg vitellin is always associated with, and probably exists 

 in combination with, the peculiar complex body lecithin (see p. 743). 



Denis, and after him, Hoppe-Seyler, have shewn that vitellin before the treatment 

 requisite to free it from lecithin, possesses properties quite different from other 

 proteids. 



A theory has been advanced that vitellin is really a complex body 

 like haemoglobin, and on treatment with alcohol splits up into coagulated 

 proteid and lecithin. When well purified it contains -75 p. c. sulphur, 

 but no phosphorus. Dilute acids or alkalis readily convert it in its un- 

 coagulated form into a member of Class II. 



Fremy and Valenciennes 2 have described a series of proteids, viz. ichthin, 

 ichthidin, &c., derived from fish and amphibia. They appear to be either identical 

 with, or closely related to, vitellin. 



Preparation. Yolk of egg is treated with successive quantities of 

 aether, as long as this extracts any yellow colouring matter ; the residue 

 is dissolved in moderately strong (10 p. c.) sodic chloride solution, and 

 filtered. The filtrate on falling into a large excess of water is 

 precipitated. In this state it is mixed with lecithin and nuclein, and in 

 order to free it from these it was usually treated with alcohol. This, 

 as above stated, entirely changes the vitellin into a coagulated form. 

 It seems probable that the separation of vitellin from the other bodies 

 with which it is mixed in the yolk of egg may be effected by precipitat- 

 ing the sodic chloride solution by the addition of excess of water ; the 

 precipitate is then re-dissolved in 10 p. c. solution of sodic chloride and 

 the process repeated as rapidly as possible 3 . 



6. Globin. 



Globin, stated by Preyer 4 to be the proteid residue of the complex body haemo- 

 globin (see p. 341), ought probably to be considered as an outlying member of this 

 class. It is however not readily soluble either in dilute acids or sodic chloride 

 solutions. It is said to bs absolutely free from ash. 



CLASS IV. Fibrin. 



Insoluble in water and dilute sodic chloride solutions; soluble 

 with difficulty in dilute acids and alkalis, and more concentrated 

 neutral saline solutions. 



1 Op. cit. - Compt. Rend. T. xxxvm., pp. 469 and 525. 



s Weyl, op. cit. S. 74. * Die Blutknjstalle (1871), S. 160. 



