150 THE AMERICAN MONTHLY [July, 



other useful medium, which dries readily hut shrinks more than the 

 others, is made by taking by weight 6 parts gum, 4 parts white sugar, 

 16 parts water, and 6 parts glycerin, prepared as described. A still 

 further modification is made by taking 8 parts gum, 4 parts white sugar, 

 2 parts gelatine, 20 parts water and 12 parts glycerin. Dissolve the 

 gelatine first, then add the gum and sugar, and lastly, the glycerin. 

 This mass never dries completely hard, but only to a tough, leathery 

 consistence. In all cases a little gum camphor, phenol, clove oil, or 

 thymol should be added to the completed mass to prevent fungoid 

 growth. 



In the preparation of Farrant's medium on any formula, much time 

 and annoyance may be saved by making the watery solution of gum, 

 etc., much thinner than it is required to be, and after filtration evapo- 

 rating it to the consistence desired and then adding the glycerin. I 

 always add to the water in the beginning an ounce or so of a weak 

 solution of chloral hydrate, and add gum thymol to the finished mass, 

 a piece the size of a large pin head will do for an ounce of medium. 



In mounting in any of these gum media, much trouble is saved by 

 first macerating the object in some of the thin medium for a longer or 

 shorter time according to its nature — longer for dense objects than for 

 thin ones — and then arranging the object on the slip in some of the 

 thin medium, allowing most of the water to evaporate (protected from 

 dust) , and then adding the thick medium and applying the cover, 

 using a light spring clip to retain it in place. Air bubbles will not be 

 included by this method. 



If a surplus of the medium was used so that much has escaped 

 around the cover, this excess should be cleaned away within 24 hours 

 after the coverwas placed, while it is still softand tough. If thecleaning 

 is delayed until the mass outside the cover is hard, the cover will often 

 be moved or pulled out of position by the removal of the outer mass. 

 As soon as the partially cleaned slide has become quite dry, the slip 

 should be placed on a turntable, and the slide cleaned close up to the 

 cover, using a knife blade or chisel-point to cut away the gum, and a 

 moist rag or folded blotter to finish. Then add successive finishing 

 rings of some resinous cement. Qbjects thus mounted will prove as 

 durable as balsam mounts ; there will be no shrinking or distortion of 

 soft parts as often occurs with objects in glycerin ; the most delicate 

 and colorless of structural details are well shown, and the objects 

 photograph extremely well. 



Air bubbles need not be included in the mount, but if unfortunately 

 present they may be removed by placing the slide in a beaker or glass 

 vessel in which it can lie flat, putting in distilled water to cover the 

 slide, and after standing a few minutes place the vessel on a sand bath, 

 when the bubbles will soon emerge from under the cover and rise to 

 the surface of the water, the slide is then to be carefully removed, wiped, 

 and some of the thick medium spun round outside the edge of the cover, 

 which will, in drying, fill the space under the cover without admitting 

 any air. This is much better than to remove the cover or to try to 

 poke out the bubbles, as the removal or displacement of the cover is 

 very liable to tangle up and destroy the object. 



