1898.] of " Connecting Threads" in the Cell Wall. 507 



violets suitable for the above reaction, and has found that the 

 methyl violet manufactured by Merck and known as Pyoktanin, 

 (a chlorhydrate of pentamethyl and hexamethyl pararosanilin) 

 gave the best results. 



I may add that Gentian violet gives almost (if not quite) as 

 good results as Meyer's Pyoktanin. 



Meyer's method has lately been used with success by Kohl 1 in 

 demonstrating the " connecting threads " in the epidermal cells 

 of Vise um album and in the parenchyma cells of the "leaf" of 

 Milium undulatum and other mosses. 



On repeating the experiments of Meyer it is easy to see that 

 the method is an admirable one and is a great advance upon any 

 of the analogous methods which have preceded it. Moreover 

 Pyoktanin has excellent staining powers and constitutes a reagent 

 of the first rank for investigations of this kind. 



Meyer's method has however certain drawbacks, which become 

 apparent when actual experiments are made, and they may be 

 summarised as follows. 



1. Want of delicacy and control. 



2. Want of certainty and uniformity of results. 



3. The formation of the lodine-Methyl-Violet precipitate. 



4. The use of fresh tissue. 



One finds in practice that it is difficult to arrange with certainty 

 that the union of the Pyoktanin and Sulphuric acid shall take 

 place in the neighbourhood of the section, and even when this is 

 accomplished, the varying proportions of the acid and the dye 

 may end in the formation of either a propitious or unpropitious 

 mixture, which in consequence may or may not stain in the 

 proper manner. The somewhat voluminous blue-black precipitate 

 which accompanies the union of the two liquids is an impediment 

 to observation, and too frequently a group of granules appears at 

 the identical place one wishes to examine. The results produced 

 by the final treatment with water are by no means uniform, and 

 one has frequently to perform the whole process over again. 

 Finally the use of fresh material involves the possibility of 

 structural changes during the cutting and manipulation, as well 

 as inability to be independent of times and seasons. 



The chief drawbacks to which I have alluded are not uncon- 

 nected with the fact that the various operations of killing, fixing, 

 swelling and staining are carried on simultaneously. In the 

 modification I am now about to describe these operations are 

 conducted apart, so that the whole process involves several 

 separate stages, and each stage can command its own special 



1 Kohl. Dot. Central. Bd. lxxii. No. 8. 1897. 



