88 PHYSIOLOGICAL CHEMISTRY. 



itates the casein. Like the other nucleo-albumins, casein leaves 

 a pseudo-nuclein residue on digestion with pepsin and hydro- 

 chloric acid. 



VITELLIN. While white of egg contains essentially albumin 

 proper and globulin, the yellow part is extremely complex, 

 containing many substances. At least two of these compounds 

 .hold phosphorus in combination; one of these is lecithin, re- 

 ferred to earlier, and the other is the nucleo-albumin called 

 'viteUin. The separation of these substances from each other 

 is extremely difficult. Vitellin is not soluble in water, but 

 dissolves in weak alkali solutions ; on digestion with pepsin and 

 hydrochloric acid it yields a pseudo-nuclein residue which con- 

 tains iron as well as phosphorus. The name hematogen has 

 been given to this, and it is considered as of great physiological 

 importance because of its iron content. It is possibly one of 

 the parent substances of hemoglobin. 



Vegetable Nucleo-albumins. Most of the protein bodies 

 thus far referred to have belonged to the animal kingdom, but 

 as plant constituents fully as great a number occur. The exact 

 nature of some of these is obscure, but many valuable obser- 

 vations have been made by Osborne and other chemists in the 

 last few years which have cleared up some of the points in 

 dispute. Only brief mention can be made here. 



In wheat flour, for example, four or five protein bodies 

 appear to be present. The most abundant of these is called 

 by Osborne glutenin and makes up over 4 per cent of the 

 weight of the grain. Next in abundance is another important 

 compound known as gliadin, amounting to about 4 per cent 

 of the grain weight. These two proteins unite in the forma- 

 tion of gluten which is essential in the production of an elastic 

 dough, which on leavening yields a porous and light bread. 

 Gliadin is soluble in dilute alcohol and forms an opalescent 

 solution with water. In some respects it resembles a gloimlin. 

 In its behavior with weak alkalies glutenin bears some resem- 

 blance to casein. Wheat flour contains also a true globulin in 

 small amount. 



