THE NITROGEN COMPOUNDS 57 



ined. The principal ones to be mentioned are gliadin 

 from wheat, zein from corn, and hordein from barley. 

 Gliadin is more abundant in the wheat kernel than is the 

 glutenin with which it is associated, the two together 

 constituting over 80 per cent of the total proteins of that 

 cereal. The proportion of gUadin in wheat flour has much 

 to do with its quality for bread-making purposes. It ap- 

 pears that the best bread flour contains about twice as 

 much gliadin as glutenin. 



72. Albuminoids. — ^This term, according to the classi- 

 fication still in more or less use in the United States, has 

 been understood as including various proteins such as 

 the albumins, and globulins. The classification now 

 recommended confines the term to proteins found chiefly 

 in the animal body in such parts as the cartilages, bones, 

 feathers, hair, hoofs, horns, and nails. These proteins 

 are also obtained from the threads of silkworms and from 

 sponges. The albuminoids have group names, such as 

 collagen in cartilage and bone, keratins in feathers, hair, 

 hoofs, horns, nails, and similar exterior tissues, fibroin 

 in the threads of silkworms, and spongin in the frame- 

 work of sponges. 



Gelatine, so well known to the housewife, is derived 

 from collagen. When meat containing tendons (cartilage) 

 is submitted to the action of boiling water, there is 

 obtained in the extract a gelatinous substance which 

 becomes evident when the extract is cooled. This gela- 

 tine is insoluble in cold water, but dissolves in hot. As a 

 dry commercial article, it is a tenacious substance which, 

 when prepared in thin layers, is transparent. When col- 

 lagen and gelatine are acted upon by tannic acid, as, for 

 instance, when the skin of an animal is treated with an 

 extract from hemlock or oak bark, the result is a sub- 



