66 BOTANICAL GAZETTE. 



scopist, but I have been somewhat surprised at the hmited number 

 who have fairly succeeded in differentiating the tissues. 



In my own experience, I have met with some sections which ob- 

 stinately refused to act as they should, under the operation of the two 

 colors, but even these, with patient manipulation, can be induced to 

 show some results, even though they may not exhibit that sharpness 

 and purity which it is the aim and object of the mounter to obtain. 



I think that a writer in Science Gossip has come nearer to the 

 true laws governing the process, than any one who has written on the 

 subject; he has, at least, indicated the direction in which the practical 

 worker must look to attain success. My own theory differs sh'ghtly 

 from his, and consequently my process varies somewhat, but in the 

 main it is the same. 



It seems to me that the capacity for staining tissues resides more 

 in the colors than in the tissue itself. A stain may be permanent, 

 unless it is driven out. It may be driven out by some solvent, by 

 some bleaching process, or lastly by some other color. Some tissues 

 hold the stain more tenaciously than others, probably on account of 

 their varying density. Thus the spiral and bass-cells will retain a 

 color longer under the influence of a solvent, than the softer and 

 more open parenchymal cells. I endeavor to take advantage of this 

 property, by giving the whole tissue all of one clor that it can be in- 

 duced to take, and then driving it out of the parenchymal tissue by a 

 stronger color, stopping the process at the moment when the second 

 color has completely replaced the first color in the soft tissues, and 

 before it has begun to act upon the more dense cells. If a section be 

 stained with roseine, and then be left long enough in a solution of 

 Nicholson's blue, the whole section will be blue, with no visible trace 

 of red. If it be taken out before the blue has permeated the entire 

 tissue, the red will show, in some parts, quite clear and well defined 

 among the surrounding blue tissues. Following out this principle, 

 that exact point must be determined when the blue has gone far 

 enough. 



In practice I carry out my theory as follows : I use a two-grain, 

 neutral solution of eosin, and in this I preserve my prepared sec- 

 tions until I am ready to use them. They keep perfectly well in this 

 solution, and are always ready to undergo the final process, which re- 

 quires but a very short time before they can be placed, fully finished, 

 under the covering glass. After taking them from the eosin solution, 

 I pass them through 95 per cent alcohol, merely to wash off the super- 

 fluous color, and then place them in a half-grain solution of Nichol- 

 son's blue, made neutral. The time required in the blue solution va- 

 ries with different tissues, and in the nice adjustment of this time, lies 

 the whole success of the operation. I generally spoil three or four 

 sections of each kind in determining the exact time required. I take a 

 section from the eosin, holding it lightly in a pair of forceps, rinse it 

 off rapidly in alcohol, and then immerse it in the blue, still in the for- 

 ceps, while I count, "with moderate haste," ten. Then quickly place 

 it in clean alcohol, and brush lightly with camel's hair brush. The 

 immersion in clean alcohol seems to check the operation of the blue in- 



