Chemical Constituents of the Animal Body. 231 



acids on hydrolysis and contain less nitrogen (1819 per 

 cent.). They also have a somewhat limited distribution, 

 and are found in certain fish-roes and globin, the protein 

 derived from haemoglobin ; the red pigment of blood is 

 also generally considered as a protein (see below). 



(c) The Albumins. These are proteins soluble in 

 water and less basic than the histones, yielding a smaller 

 percentage of diamino-acids on hydrolysis and containing 

 only about 15 per cent, of nitrogen. They are found 

 largely in animal tissues, the albumins of egg-white and 

 blood-serum being typical examples. They are not pre- 

 cipitated from solution by magnesium sulphate, but are 

 precipitated by saturating their aqueous solutions with 

 ammonium sulphate. 



(d) The Globulins. Proteins of this class are widely 

 distributed in both the animal and the vegetable world. 

 They are insoluble in water, but soluble in salt solutions 

 of somewhat low dilutions, from which they can be precipi- 

 tated by saturation with magnesium sulphate or half- 

 saturation with ammonium sulphate. As examples of 

 globulins may be cited the globulins from blood-serum 

 and edestin, a vegetable protein from hemp seed. These 

 two examples may, perhaps, illustrate the artificial char- 

 acter of the classification of the proteins adopted, as, apart 

 from their solubility in salt solutions and insolubility in 

 pure water, the two substances have little in common. 



(e) The Alcohol Soluble Proteins or Prolamines. 

 Only a very few members of this class are known, but 

 gliadin, the chief constituent of wheat gluten, is an im- 

 portant protein. This substance is insoluble in water and 

 absolute alcohol, but is readily soluble in a mixture of 

 the two fluids. The best solvent is 70-80 per cent, 

 alcohol. It is characterized by the large amount of 

 ammonia it yields on hydrolysis (or amide nitrogen, see 



