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209 



PRACTICAL PHYSIOLOGY, 



PART I. CHEMICAL PHYSIOLOGY, 



LESSON I. 

 THE PROTEIDS. 



As a type of the group of proteids we may take white of egg, egg- 

 white, or egg-albumin. In nature they occur only as constituents 

 or products of living organisms. In animals they form the prin- 

 cipal solids of the muscular, nervous, and glandular tissues of 

 blood-serum and lymph. The bile, urine, tears, and sweat, are the 

 only animal fluids which normally do not contain proteids. Their 

 elementary composition varies within the following limits : 



C. H. N. 0. S. 



From 50 68 15.0 22.8 0.4 per cent. 

 To 55 7.3 18.2 24.1 5.0 ,, 



They are amorphous, and for the most part colloid bodies. They 

 possess certain chemical reactions in common, and are closely 

 related to each other. They are insoluble in alcohol and ether, 

 some are soluble in water, others insoluble, while others are soluble 

 in weak saline solutions. They all rotate the ray of polarised light 

 to the left, and are thus Isevorotatory. In strong acids and alkalies 

 they are dissolved, but they mostly undergo decomposition in the 

 process. When decomposed, they yield a very large number of other 

 bodies, so that their constitution is exceedingly complex. In the 

 body, after undergoing a series of metabolic changes, they are ex- 

 creted chiefly in the form of urea, and a number of more or less 

 closely related nitrogenous bodies. Besides the general characters 

 stated below, most of them yield aromatic bodies, such as tyrosiii 

 and phenol. 



