302 PROTEINS 



may readily be stained in fuchsin. To do this, the sections 

 should be placed in a '2 per cent aqueous solution of acid 

 fuchsin for twenty-four hours, washed in running water and 

 mounted in Canada balsam in the usual way. 



Several proteins may occur in aleurone grains and may be 

 recognized by their different solubilities in water, salt solution, 

 alkali, and alcohol. Also, the details of the composition of 

 these grains are not the same for all plants in which they 

 occur; for instance, in the Paeony the matrix is soluble in 

 water, whereas in the castor-oil plant it is insoluble in water, 

 but soluble in a strong aqueous solution of sodium phosphate. 



According to Bokorny,* globulins are the common pro- 

 teins occurring in the aleurone grains and crystalloids of 

 seeds. It should be remarked that the term aleurone grain 

 is frequently used in a generic sense to include all non-crys- 

 talline reserve protein bodies of a more or less definite shape ; 

 they are not always of the complicated nature described above, 

 thus in the grain of wheat they are quite simple in structure 

 and do not contain a crystalloid nor a globoid. -f 



GENERAL PROPERTIES OF PROTEINS. 



Until recently, comparatively little was known with regard 

 to the chemical nature of proteins beyond the fact that they 

 were composed of the elements carbon, hydrogen, nitrogen, 

 oxygen and sulphur, together with, in some cases, phosphorus 

 and iron ; their existence as a separate group of compounds 

 therefore depended chiefly on their sharing a number of general 

 physical and chemical properties, without regard to their con- 

 stitution, concerning which little or nothing was known. 



A scientific definition of proteins was first given by Panzer,^ 

 who classified as proteins all substances which on hydrolysis 

 yield mono- or di-amino acids. This definition is, however, 

 too comprehensive, as it would include amongst the proteins 

 the group of substances described by Fischer as polypeptides. 



The general physical and chemical properties which are 

 shared by the typical unaltered proteins, such as albumins and 

 globulins, may be summarized as follows : — 



* Bokorny : " Bot. Centrbl.," igoo, 82, 289. 



+ For an account of the artificial production of pnotein grains, see Thompson : 

 " Bot. Gaz.," 1912, 54, 336. 



X Panzer : " Wiener kUn. VVochenschr.," 1903, 16, 689. 



