IODINE. 7 



brown. This is 'especially true of the nucleus and 

 chlorophyll bodies, as well as of the nitrogenous 

 fundamental part of the protein grains, for the 

 detection of which a rather concentrated solution 

 should be , used. Since a very small quantity of 

 iodine is quickly fatal to protoplasm, besides col- 

 oring it, this reagent is especially useful in study- 

 ing bacteria and other ciliated micro-organisms. 

 In the study of protein grains the glycerine solu- 

 tion is best, because of its clearing action. 



The starch I which occurs in chlorophyll bodies is 

 easily detected by treating very thin sections with 

 alcohol, or potassic hydrate and acetic acid, and 

 afterwards adding a solution of iodine in water 

 which contains potassic iodide, when the swelling 

 starch grains assume the characteristic blue color. 



The so-called crystalloids consist of protein sub- 

 stances, and consequently turn yellow when treated 

 with iodine. This is also the case with inuline, 

 where, however, the color does not depend upon a 

 real imbibition of the iodine, but only upon a con- 

 densation of the brown fluid in the fine fissures of 

 the sphaero-crystals. 



All objects colored with iodine fade in the 

 course of time ; and iodine solutions destined for 

 use should be kept in the dark, to prevent the 

 formation of hydriodic acid, which is greatly pro- 

 moted by the action of light. When sections or 



1 Sachs: JahrbUcher fiir wiss. Bot, 1863, III., p. 200; Flora, 1862, p. 

 166. Weiss: Allgem. Bot., 1878, 1., p. in. 



