CHAPTER V. 

 THE PROTEIN SUBSTANCES. 



These 'extremely important bodies, usually called albumi- 

 nous bodies, are found in vegetable and animal organisms of 

 all kinds and in some form are essential elements in cell 

 growth. Unlike the fats and carbohydrates they seem to be 

 elaborated in the vegetable kingdom only ; or, at any rate, the 

 fundamental structures in them appear to be formed in vege- 

 table growth only. The animal is able to modify and trans- 

 form to some extent, but apparently can not build them up 

 from simple materials. In composition the protein bodies are 

 extremely complex; qualitatively they contain carbon, hydro- 

 gen, oxygen, nitrogen and sulphur. In an important group 

 of these bodies phosphorus is also present and a few contain 

 iron. The quantitative composition of some of the best known 

 protein compounds is expressed approximately as follows : 



Per Cent. 



C 50.0-55.0 



H 6.5- 7-3 



O 19.0-23.0 



N 15.0-17.0 



S 0.3- 2.4 



Attempts have been made to calculate formulas for certain 

 protein bodies from the results of analyses, but no great impor- 

 tance attaches to the empirical formulas so reached. The 

 best analyses made of the compounds differ among themselves 

 to an extent that makes a definite result quite impossible. 

 This is largely due to the fact that there are great practical 

 difficulties in the way of properly purifying the substances as 

 a preliminary to analysis; they all occur mixed with other 

 compounds, such as fats, carbohydrates and mineral matters, 

 and to remove these without in any way altering the compo- 



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