NARCEINE — NUCLEUS 353 



Millon's reagent, while the surrounding cells may be stained 

 a pale rose color. When sections containing myrosin are heated 

 in a concentrated solution of hydrochloric acid which contains 

 a drop of a lo per cent, aqueous solution of orcin in each cubic 

 centimeter, a violet color is produced in the cells containing the 

 myrosin. Myrosin produces allylic mustard oil from potassium 

 myronate, a glucoside which occurs in the parenchyma cells 

 which are associated with those containing myrosin. 



Narceine, C23H27N08 + 3H,0.— This is an alkaloid oc- 

 curring associated with morphine in the latex of Papaver som- 

 niferum. When a yellow color follows the addition of meth- 

 ylal to the latex, the presence of narceine is indicated. 



Narcotine, C22H23NO7. — An alkaloid associated with mor- 

 phine in opium. Sodium selenate produces with it an orange- 

 red color. 



Nicotine, CjqHj^Nj. — The alkaloid occurs in most species 

 of Nicotiana, especially in N. Tabacum. It has not been found 

 outside this genus. When sections containing nicotine are 

 treated with potassio-mercuric chloride, a yellowish-white pre- 

 cipitate is produced. Phospho-molybdic acid gives, with nico- 

 tine, an abundant yellow precipitate. In the presence of nico- 

 tine mercuric chloride produces a white, and platinum chlo- 

 ride a yellow, precipitate, while potassium iodide-iodine causes 

 first a carmine-red color and finally a reddish-brown precipi- 

 tate, which gradually bleaches out. 



Nitrates. — ^When nitrates are present in a solution, a drop 

 of barium chloride added to a drop of the solution will produce 

 a precipitate of octahedral crystals of barium nitrate. See 

 also under Diphenylamine in the last chapter. 



Nucleus. — The nucleus can best be demonstrated in tissues 

 which have been fixed according to the directions given under 

 Fixatives in the last chapter. Also under Iodine-green and 

 Acetic Acid, and Methyl-green and Acetic Acid, are given direc- 

 tions for instantly fixing and staining nuclei. The three-color 

 method of staining detailed on page 264 gives the best results for 

 the dividing nucleus. 



