50 CELL-CONTENTS AND CELL-WALLS. 



add a few c.c. of amyl alcohol, and shake, then allow to stand 

 the amyl alcohol separates, coloured red or violet. This reaction is 

 due to the presence of the amino acid tryptophane. 



(c) Concentrate some of the liquid to small bulk by heating on a 

 water bath ; after a day, examine the residue with the microscope 

 for crystals of leucin and tyrosin. The leucin is chiefly in 

 brownish spheres showing radiate and concentric markings, the 

 tyrosin in bundles or rosettes of long white needles. 



(d) The leucin is also obtained as a sticky residue if the filtered 

 liquid is treated with alcohol until no more precipitate comes down ; 

 filter and concentrate the filtrate on a bath. 



(e) Treat a portion of the filtered liquid with Millon's reagent, 

 which precipitates any proteins present ; filter, and boil the filtrate 

 ^a red colour indicates tyrosin. 



6O. Amino Acids and their Derivatives. The 



amino compounds (amines, amino acids, amides), con- 

 taining carbon, hydrogen, oxygen, nitrogen, and in some 

 cases (cystin) also sulphur, may be formed either in con- 

 structive or in destructive metabolism. That is, they are 

 intermediate bodies formed either on the up-grade towards 

 protein, or on the down-grade from protein to simpler 

 bodies. In either case they are important for transloca- 

 tion, being soluble and diffusible. Many of these sub- 

 stances are present in plants e.g. asparagin, which is 

 abundant in seeds of Leguminosae. Asparagin (and other 

 amino compounds) combines with non-nitrogenous sub- 

 stances to form proteins ; it often accumulates in those 

 parts of plants where there is not sufficient non-nitrogenous 

 material at hand for the formation of proteins, Asparagin 

 may accumulate in plants which are grown in darkness, so 

 that photosynthesis cannot take place. Lupin seedlings 

 germinated in darkness contain a large amount of aspara- 

 gin, which disappears when the seedlings are placed in the 

 light. If, however, the seedlings are exposed to light in 

 an atmosphere deprived of carbon dioxide, the asparagin 

 persists in the seedlings. Both asparagin and tyrosin 

 occur in Dahlia tubers. Leucin is associated with aspara- 

 gin in seedlings of Lupin and other Leguminosae. In 

 Cruciferae, Cucurbitaceae, etc., asparagin is replaced by an 

 allied substance, glutamin. 



