10 PRINCIPLES OF FEEDING FARM ANIMALS 



The proteins arc composed of the elements carbon, 

 hydrogen, oxj'-gen, nitrogen, and usually sulphur in varying 

 proportions. Some proteins also contain phosphorus, while 

 other elements are found sometimes. The typical protein 

 molecule usually contains from 15 to 19, or an average of 

 16 per cent of nitrogen, 52 per cent of carbon, 7 per cent 

 of hydrogen, 22 per cent of oxygen, and 0.5 to 2 per cent 

 of sulphur. The chemical structure of the protein molecule 

 is very complex, and neither the formulae nor molecular 

 weights of any of the proteins have been determined defi- 

 nitely. An idea of their complex nature may be obtained 

 from the following approximate formulae of some common 

 proteins : egg albumin, C696H1125N175S6O220 ; serum albumin, 

 C'694 H1045N175S2O225 ; oxyhemoglobin, C656Hii6iN207S2Fe02io. 



However, it has been determined that the complex pro- 

 teins are made up of amino acids, which are comparatively 

 simple organic acids in which one or two " amino," or 

 NH2 groups are substituted for an equal number of hydrogen 

 atoms. There are 18 or more of these amino acids known. 

 Some of them occur in all proteins; others are absent, or 

 are present in only small amounts, in certain proteins. 

 Furthermore, different proteins may be formed from the 

 same amino acids arranged in different combinations. 

 Thus one finds that the proteins are very numerous. The 

 amino acids have been compared to the letters of the alphabet. 

 " When they are arranged together they can make many 

 different proteins just as there are many different words in 

 the dictionary." ^ 



There are considerable differences in the nutritive values 

 of the different amino acids, some of them being essential 



^ Lusk, " The Basis of Nutrition," p. 17. 



