250 PHYSIOLOGY OF NUTRITION. 



slum sulphate produced. The sections are placed in one of the 

 Copper solutions, removed after a few minutes with the forceps, 

 superficially washed by dipping 1 in clean water, and then at once 

 laid in potash solution which is heated to boiling'. The contents 

 of the cells take on a violet coloration in virtue of their proteid 

 contents.* 



If a section from the cotyledon of a dry pea is mounted on a 

 slide in a drop of glycerine (2 parts of glycerine to 1 part of 

 water), covered with a cover-glass, and treated from the edge of 

 the cover-glass with a drop of Iodine solution, the starch grains 

 at once take on a, blue coloration, but the aleurone grains, and 

 the ground mass in which they are embedded, become yellow 

 owing to their richness in proteid. 



In contact with sugar and Sulphuric acid proteids become red 

 in colour, and to familiarise ourselves with this reaction we mount 

 sections, e.g., from the cotyledons of a dry bean in a drop of con- 

 centrated cane-sugar solution, and run in strong Sulphuric acid 

 from the margin of the cover-glass. 



If sections from plant structures rich in proteids are placed on 

 a, slide for some minutes in a drop of cold fuming Nitric acid, and 

 then treated with ammonia, they take on an intense yellow colour 

 (Xanthoproteic reaction). 



Millon's reagent stains proteids brick-red. It is prepared by 

 treating mercury, without warming, with an equal part by weight 

 of concentrated fuming Nitric acid, and diluting, after the metal 

 has dissolved, with an equal volume of water. It is advisable 

 only to use the reagent when freshly prepared. If we place 

 sections from the cotyledons of Pisum in a drop of the reagent, if 

 necessary slightly warmed, the contents of the cells become dis- 

 organised; after a time, however, owing to the presence of pro- 

 teids they stain brick-red. 



In recent years numerous reagents (particularly solvents) have 

 been used for acting on the protoplasmic structures of cells, and 

 on the results obtained has been based the view that a whole 

 series of different proteid substances are present in the protoplasm, 

 cell-nucleus, etc. It is, in fact, certain that, e.g., nuclein, as we 

 shall see in 97, has properties quite different from those of an 



* This reaction, however, like others, is not absolutely decisive. The test 

 may also be made by laying the sections on the slide in a drop of Febling's 

 solution, covering with a cover-glass, and heating till the formation of bubbles 

 ceases. 



