THE NUTRIENTS AND NUTRITION 303 



Commercial meat scrap, on tlie other hand, is well siippHed 

 with cystin. Experiments in ]jrogress at the Kansas Station 

 indicate that possibly the lack of cystin in casein is a limiting;; 

 factor, when caseiji is used as the main source of protein in 

 the laying ration. 



It is because of the fact that nitrogen is an absolute 

 essential to animal life that the nitrogenous compounds are 

 called "protein," a term adapted from the Greek word 

 meaning "to be first." Besides nitrogen, protein compounds 

 always contain carbon, hydrogen, and oxygen, and some- 

 times contain sulphur, phosphorus, and iron. 



As will be seen by referring to Table XXXV, over 21 per 

 cent of the entire body of a Leghorn hen is protein, while it 

 constitutes 48.9 per cent or nearly half of the total dry 

 matter. While it forms but 12.83 per cent of the new-laid 

 egg because of the large amount of water and ash, it will 

 be noticed that it constitutes 49.8 per cent of the dry matter 

 of the contents of the egg. 



In the fowl's body the muscles, skin, feathers, tendons, 

 brain, blood, and internal organs are composed mainly of 

 protein. The dry matter of the white of the egg is nearly 

 94 per cent, protein, while that of the yolk is over 34 per cent 

 protein. 



Lewis' found that laying hens fed a ration deficient in 

 protein not only gave a low production but that the eggs 

 produced were undersized. 



Egg white shows very nicely some of the characteristics 

 of protein compounds. In analysis it approaches very closely 

 the average analysis of proteins as given by Sherman i^ 



Carbon. Hydrogen, Oxygen, Nitrogen, Sulphur, 

 per cent per cent per cent per cent per cent 



Average analysis of proteins 53.00 7.00 23.000 16.00 1.000 



Analysis of egg white . 52.75 7.10 23.024 15 51 1.616 



When dry it forms a horny substance which decomposes 

 in the flame, forming a black mass. At the same time fumes 

 are given off, which smell like liurning hair or feathers. When 



I New .lerscy Pmllrtin, No. 205. 

 ^ Chemistry of Food and Nutrition. 



