Reagents and Processes. 387 



in order to keep it from cracking across the other specimens in the 

 block. 



The paraffin bath can be simply made and operated as follows : 

 Nearly fill a tumbler or other relatively tall dish with melted paraffin, 

 and after the paraffin has hardened, set a copper plate over the tumbler, 

 and leave one corner of the plate projecting far enough to permit a 

 Bunsen burner or kerosene lamp to be placed under it. The flame 

 should be kept at a height to melt the paraffin to a depth of about half 

 an inch. When the material which has been gradually brought into con- 

 centrated paraffin as above directed is poured into the melted paraffin 

 of the bath, it will sink to the bottom of the melted portion, where its 

 infiltration will be completed just at the temperature of the melting 

 paraffin ; which is as it should be. 



The object of gradually bringing the material into a solvent of par- 

 affin and of infiltrating with paraffin slowly is to keep the protoplasts 

 from shrinking together and to make the infiltration more complete. 



Iodine Solution. Dissolve 0.5 gram of potassium iodide in a few 

 cubic centimeters of water, and add iodine until no more can be taken up. 

 As a reagent for starch, dilute to a light brown color. For demonstrat- 

 ing proteids and protoplasts, dilute much less than for starch, namely, 

 to a red-brown color. By this reagent, starch is stained violet to dark 

 blue, and proteids and protoplasts yellow to brown. Lignified, cutin- 

 ized, and corky membranes are stained yellow. 



Lime Water. Pound up unslaked lime ; place this in a bottle to 

 one-third its capacity, fill the bottle with water, cork* it and shake 

 thoroughly. Keep the bottle stoppered, and after the lime has settled 

 decant or filter off the clear liquid. Keep in a tightly stoppered bottle. 

 Used to demonstrate CO 2 , which combines with it to form a white pre- 

 cipitate of calcium carbonate. 



Phloroglucin. Dissolve in 15 cubic centimeters of 95% alcohol as 

 much phloroglucin as is held on the point of a penknife. Use as a 

 test for lignified membranes in the following manner : Place the mate- 

 rial to be studied in the solution for a few moments ; then transfer to a 

 drop of water on a glass slip, and put on a coverglass. Place a drop 

 of concentrated hydrochloric acid on the slip in contact with the cover- 

 glass. As the acid diffuses through the water, the lignified membranes 

 will be stained pink. 



The cellulose tissues of the section may now be stained purple by 

 replacing the reagent under the coverglass with chloroiodide of zinc. 



