THE MICROSCOPE. 



Let us then commence with the axiom that all fluid mounts 

 must be made in a cell, properly constructed of materials which will 

 resist the action of the fluid, and of sufficient depth to entirely sub- 

 merge the specimen, so that the latter shall exert no upward or lift- 

 ing action upon the cover. The latter is of special importance, 

 since if the slightest pressure be necessary to force down the cover 

 upon the walls of the cell, the continued pressure of the confined 

 specimen will in a short time raise it and cause a leak. 



The best material for making cells for fluid mounts, where 

 those deeper than can be made with cement alone are required, is 

 undoubtedly glass, attached to the slide by marine glue. They are 

 absolutely permanent and leave nothing to be desired save that they 

 were less costly. But they are necessarily so, and for this reason 

 are comparatively little used. Block tin is also an excellent ma- 

 terial, and cheaper than glass, but it is heavy and not so readily or 

 securely cemented to the slip as the latter. I have not had sufficient 

 experience in its use to give any opinion as to its resisting the action 

 of all the mounting fluids usually employed, but feel sure it is quite 

 safe against glycerine or camphorated water. 



In my own practice, where a cell deeper than can be conven- 

 iently made with cement alone is required, I have for several years 

 used wax exclusively, and have had no reason to change the favor- 

 able opinion of its merits expressed in the paper I had the honor 

 to read before the American Microscopical Association at its Detroit 

 meeting in 1880. At that time I had been using the wax cells for 

 fluid mounts for some time; the three years' additional experience 

 since gained have only served to confirm my conviction that it is a 

 material deserving of the largest use for this purpose, being easily 

 prepared, entirely permanent, and so cheap as to be almost without 

 cost. To sum up then, if the tissue to be mounted be exceedingly 

 thin, requiring scarcely any cell to contain it, make the same with 

 cement alone; if a cell of greater depth be demanded, use glass 

 cemented to the slip with marine glue, if the question of expense 

 be not a serious one with you; if it is, use without hesitation the 

 wax cells (prepared as will hereafter be directed) for any ceils not 

 more than /^ inch diameter and % inch deep, and give yourself no 

 uneasiness as to their permanency. 



The essentials for making any of these cells are like those for 

 balsam mounts, neither numerous or costly, though, as the making 



