NERVOUS TISSUE. 253 



haemin (see p. 198). If the slide be permitted to stand, thus allow- 

 ing the fluid to evaporate, the crystals will disappear and leave 

 brown oily drops. They will reappear, however, upon the addi- 

 tion of fresh iodine solution. v. Stanek claims that this choline 

 compound has the formula C 5 H n4 NOI*I 8 . 



(b) Rosenheim's Bismuth Test. Extract the fluid under exam- 

 ination with absolute alcohol, evaporate and re-extract the residue. 

 Repeat the extraction several times. Dissolve the final residue in 

 2-3 c.c. of water and add a drop of Kraut's reagent. 1 Choline is 

 indicated by the appearance of a bright brick-red precipitate. 



1 Dissolve 272 grams of potassium iodide in water and add 80 grams of bis- 

 muth subnitrate dissolved in 200 grams of nitric acid (sp. gr. 1.18). Permit 

 the potassium nitrate to crystallize out, then filter it off and make the filtrate 

 up to i liter with water. 



