THE PROTEIX SUBSTANCES. I I I 



ELASTIN. 



Elastin differs from keratin mainly in its higher content of 

 carbon and low sulphur content. In their behavior toward 

 reagents they are much alike. Like keratin, elastin can be dis- 

 solved only by change in composition. Leucine is produced 

 in large amount by the hydrochloric acid cleavage, and glyco- 

 coll, tyrosine and other amino products in smaller amount. 

 Subjected to peptic and pancreatic digestion elastin is slowly 

 dissolved, yielding albumins and a kind of peptone. Most of 

 the protein reactions may be obtained from elastin after bring- 

 ing it into solution with alkali. 



AMYLOID SUBSTANCE. 



This is a body which is found in the so-called amyloid de- 

 generation of the liver and kidney. It is particularly charac- 

 terized by the reddish brown color it assumes when heated 

 with a solution of iodine in potassium iodide. The analysis 

 of amyloid shows a large amount of carbon and some sulphur. 

 It is insoluble in cold water, but partly soluble by long heat- 

 ing. It gives the usual protein reactions when brought into 

 alkaline solution, and contains also a complex group which 

 yields chondroitin sulphuric acid. 



FOOD STUFFS. 



In the preceding pages the individual substances used as 

 foods or occurring as essential principles of the animal body 

 have been briefly discussed. In nature these compounds do 

 not occur in the pure free condition, but are practically always 

 mixed with other compounds. Before passing to the subject 

 of digestion it will be necessary to have some idea of the gen- 

 eral composition of the ordinary foods as used by man. This 

 information will be presented in tabular form, the figures being 

 average values from tables of Atwater. The fuel values are 

 given in so-called large calories. 



