XXVII, 2. Wilson : Improved methods of utilising organised structures. 233 



heating of the slide is perfectly uniform throughout. When the tray 

 is not in actual use it should be covered by a sheet of glass, upon 

 which the volatilised mercury will condense in a fine film of globules, 

 which can be cleaned off from time to time. 



If it be desired to flatten sections which have been doubly- 

 embedded in celloidin and paraffin , a much deeper tray or glass 

 box may be used, covered with an accurately fitting lid, the bottom 

 being covered to the same depth as in the previous case. When 

 the slides of sections have been placed on the mercury at the bottom 

 of this box a small pledget of cotton wool is saturated with ether 

 and placed in one corner , away from contact with the slides , and 

 the close-fitting lid placed in position. The box is thus converted 

 temporarily into an ether vapour chamber in which the celloidin 

 tends to soften, and the sections more readily flatten out than when 

 merely floated out and warmed. It is hardly necessary to say that 

 in all section-flattening methods the temperature must be carefully 

 controlled so that the paraffin may not become molten. 



V. 



I have found the following a very convenient and simple expe- 

 dient for suspending blocks of tissue in fluid , and especially for 

 passing them through successive series of fluids. I use short seg- 

 ments of wide glass tubing, from 18 to 30 mm in diameter; one 

 end of such a segment is closed by mosquito netting or fine white 

 net or veiling tied round it ; the tissue is placed in this tube which 

 is then closed at the other end by a cork with a hole through it. 

 The cork must be bulky enough to float the whole in the fluid. 

 Such a floating vessel can be transferred from jar to jar with the 

 utmost readiness and without any handling of the tissue. I am 

 aware that similar arrangements have been frequently described, 

 but the above has the merit of very great simplicity and cheapness. 



If the gauze bottom of the tube, prepared as above, be dipped 

 in a 10 per cent solution of gelatine and allowed to set, it can 

 then be formalinised, and preserved indefinitely either in very weak 

 formalin solution, or in alcohol. Such a tube may then be utilised 

 as a floating differentiator. Thus, a piece of tissue may be placed 

 in it in a small quantity of one fluid , and after inserting the per- 

 forated cork it may be floated in a vessel containing another fluid, 



