694 RECORD OF CURRENT RESEARCHES RELATING TO 



double-staining vegetable tissues, the conclusion he has arrived at is, 

 that no rules can be given which will ensure success in every case. 

 The process is familiar to every working microscopist, but the limited 

 number who have fairly succeeded in differentiating the tissues is 

 somewhat surprising. In his own experience he has met with some 

 sections which obstinately refused to act as they should under the 

 operation of the two colours, but even these, with patient manipula- 

 tion, 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. 



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. The theory of the present author is 

 slightly different, and consequently his process varies somewhat, but 

 in the main it is the same. The capacity for staining tissue resides 

 more in the colours than in the tissue itself. A stain may be per- 

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

 solvent, by some bleaching process, or lastly by some other colour. 

 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 colour longer under the influence of a solvent than the softer 

 and more open parenchymal cells. He endeavours to take advantage 

 of this property by giving the whole tissue all of one colour that it 

 can be induced to take, and then driving it out of the parenchymal 

 tissue by a stronger colour, stopping the process at the moment when 

 the second colour has completely replaced the first colour 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 solu- 

 tion 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 prin- 

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

 enough. 



In practice the theory is carried out as follows : A two-grain 

 neutral solution of eosin is used, and in this the prepared sections are 

 preserved until the operator is ready to use them. They keep per- 

 fectly well in this solution, and are always ready to undergo the final 

 process, which requires but a very short time before they can be placed, 

 fully fiinished, under the covering glass. After taking them from the 

 eosin solution, they should be passed through 95 per cent, alcohol, 

 merely to wash off the superfluous colour, and then placed 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 adjust- 

 ment of this time lies the whole success of the operation. Three or 

 four sections of each kind are generally spoilt in determining the exact 

 time required. A section is taken from the eosin, holding it lightly in 

 a pair of forceps, rinsed off rapidly in alcohol, and then immersed in 

 the blue, still in the forceps, while ten can be counted with moderate 



