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 10 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, C 23 H 27 NO 8 + 3H 2 O. 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, C 22 H 23 NO 7 . An alkaloid associated with mor- 

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

 red color. 



Nicotine, C 10 H 14 N 2 . 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. 

 23 



