194 The Microscope. 



The first paper of general interest was by Dr. F. L. James, 

 of St. Louis, on 



" SHRINKAGE OF CEMENT CELLS, 



The Cause of Leakage in Glycerine Mounts" 



We clip the following account of this paper from The Na 

 tional Druggist: u Di\ James stated that all of the cements 

 usually used by microscopists for cell building, with but few 

 exceptions, consist of some gummy or resinous substance dis- 

 solved in a volatile medium, consistency being given to the so- 

 lution by the admixture of some solid pulverulent matter. A 

 typical cement of this description, and the best of all cements 

 for general purposes in cell building, is that known as white zinc 

 cement, which is made by dissolving gum damar in benzol and 

 adding pure ozide of zinc to the solution. When this cement is 

 properly made at least 50 per cent, of the entire bulk of the 

 fluid should consist of zinc oxide, 10 to 15 per cent, of the damar 

 gum and the balance, from 35 to 10 per cent, of volatile benzol. 

 It is manifest that such a liquid, on exposure, would lose benzol 

 by evaporation, and that this loss would affect the bulk and di- 

 mensions of any cell built with it, Dr. James had devised a 

 very simple instrument for making visible the extent of the 

 shrinkage through which a cell built of this material passes in 

 drying, but which he did not have ready for exhibition. He, 

 however, made a blackboard drawing of the instrument and ex- 

 plained its method of action to the society. 



With these facts staring them in the face there are men en- 

 gaged in microscopical technological work who reason on cause 

 and effect so little that they are in the habit of making cells 

 of white zinc cement, rilling them with incompressible materi- 

 als, and sealing them up in their fresh and unshrunken state. 

 When the inevitable result of such a proceeding comes, as it 

 always does, and the incompressible fluid, subjected to the pres- 

 sure of the shrinking cell walls, forces its way out of them and 

 escapes, they are astonished and wonder " why it is that glycerine 

 always will creep," or get angry and damn white zinc cement 

 as being utterly unreliable. But just as it is usually the poor 

 mechanic who complains of his tools, so it is the thoughtless and 

 unreasoning technologist or experimenter who fails to get satis- 



