1899] MICROSCOPICAL JOURNAL. 15 



very penetrating glycerine would soon have found its way 

 through. This is the general principle, varying the var- 

 nishes as circumstances and the mounting fluid require. 

 Marine glue, much in vogue for securing cells to glass, has 

 failed to stand the test of time ; india-rubber compounds 

 are notoriously unstable. For fixing glass cells on slips 

 I have made a firm joint with a mixture of red lead and 

 white lead after the manner of the blacksmith's hot- 

 water joint. I take flake white from the tube and work 

 powdered red lead into it with a palette knife until it be- 

 comes too stiff to work comfortably ; I then dilute with 

 gold size only a small portion at a time as I want it, as it 

 hardens very rapidly when the gold size is added. Press 

 the cell hard down so as to have the thinnest secure film 

 of cement, and keep in a warm place for a few days; turn 

 off the surplus ooze before it has become too hard, and do 

 not use the cell for at least a fortnight. Your excavated 

 cells and solid cast ones used by Hett are of course bet- 

 ter than any built-up ones." 



It will be noticed that he advocates five or six thin 

 coats of gold size instead of one thick one. The reason 

 is that oil varnishes, after the evaporation of the turpen- 

 tine, harden not by evaporation of the oil, but by its ox- 

 idation, forming a tough layer, and therefore the process 

 goes on best in a thin layer. Finally, I would recom- 

 mend for extreme durability for fluid mounts such au 

 mine, in which the mounting fluid is formalin, or similar 

 watery fluids, first a coat of pure damar in benzole, then 

 a coat of the mixture of damar and gold size, followed by 

 three or four thin coats of pure gold size at intervals of 

 twenty-four hours, and lastly a finishing coat of Ward's 

 brown cement. The "extra stout" gold size I am inclined 

 to discard again, because it does not adhere to glass so 

 firmly as the ordinary quality. . 



DISCUSSION. 



In discussing the above paper, Dr. Measures said it al- 



