82 



THE AMERICAN MONTHLY 



[May, 



covering glass. After taking them 

 from the eosin solution, I pass them 

 through 95 % alcohol, merely to 

 wash off the supei'fluous color, and 

 then place them in a half-grain 

 solution of Nicholson's blue, made 

 neutral. The time required in the 

 blue solution varies 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 re- 

 quired. I take a section from the 

 eosin, holding it lightly in a pair of 

 forceps, rinse it off rapidly in alco- 

 hol, and then immerse it in the blue, 

 still in the forceps, while I count, 

 " with moderate haste," ten. Then 

 quickly place it in clean alcohol, 

 and brush lightly with a camel's- 

 hair brush. This immersion in clean 

 alcohol seems to check the operation 

 of the blue instantly. I then ex- 

 amine it under a one-inch objective, 

 to determine whether the exact 

 point where the blue and the red 

 remain distinct has been reached. 

 If tlie blue has not occupied all the 

 softer cells, I take another section, 

 and put it through the same pro- 

 cess, counting twelve, and so on, 

 until the proper point is reached ; 

 or, on the other hand, decreasing 

 the count, if the blue has infringed 

 upon the red in the more dense 

 tissue. Having thus determined 

 the count for tne sections of that 

 particular material, I pass the re- 

 mainder of my sections through the 

 blue into the alcohol, merely count- 

 ing off the immersion of each sec- 

 tion. I then place the sections 

 for a few moments in absolute alco- 

 hol, which seems to fix the colors, 

 then through oil of cloves into 

 benzole, and mount in damar and 

 benzole. It is sometimes advisable, 

 with delicate tissues, to merely 

 rinse off the blue in 95 % alcohol 

 and fix the colors at once in abso- 



lute alcohol, but every operator will 

 learn the minor details for himself 

 in the manipulation. 



Of course, with the " rule of 

 thumb " method of counting off the 

 time, slight variations will occur, 

 which will mar the beauty of the 

 finished product ; besides which 

 minute differences in the thickness 

 of the section will affect the result, 

 and even a distance of a quarter of 

 an inch in the same stem will make 

 a difference in the density of the 

 tissue, which will be obvious in the 

 sharpness of the colors under the 

 objective. So that the operator 

 should not be disappointed if, out 

 of a dozen slides, only four should 

 be worth preserving. The others 

 can go into the borax-pot to be 

 cleaned for another operation. 

 However, the beauty of those 

 which do pass inspection, will amply 

 repay for the labor on the spoiled 

 ones. I have perhaps been need- 

 lessly minute in the description of 

 the process I have employed, but I 

 have been so often hampered by 

 the lack of minuteness in descrip- 

 tions of processes by others, which 

 I have been endeavoring to carry 

 out, that I deem it better to err 

 upon the safe side, even at the risk 

 of being considered dry or prosy. 



One word as to the use of eosin. 

 I was attracted to it by its exquisite 

 purity of color under transmitted 

 light, and its perfect transparencv. 

 I found that sections, preserved m 

 its solution, always retained their 

 transparency, and did not become 

 clogged or thick with color, so that 

 when taken out after months of 

 immersion, the most dense cells 

 were no deeper in color than the 

 solution itself. So far as regards 

 its hold upon the tissues, it is as 

 strong as roseine, or any of the 

 heavier colors I have ever tried. I 

 cannot testify as to its permanence, 

 but I have some slides that were 



