mVERTEBRATA, CRTPTOGAMIA, MICROSCOPY, ETC. 863 



iu the microscopical journals the writers, wlio with little experience 

 have so lauded wax rings, speak of ' thin rubber ' for rings ; evidently 

 they have seen somewhere the gutta-percha mount, and supposed it 

 rubber — the latter will not answer, melted rubber will not become 

 hard. One beauty of the gutta-percha ring is the very moderate 

 heat required ; it is thus available for many objects which might be 

 injured by the greater heat necessary for the asphalt or shellac rings. 

 As tliese rings, in the arrangement which I have spoken of, can be 

 rapidly made, and as they can be kept for any length of time (shut 

 away from the dust), they are at any moment ready as well as con- 

 venient for use. The preparation is first arranged, dried or burnt on 

 the cover, the slide cleaned, a ring laid on the centre, and on this the 

 cover is placed ; the whole is now held together by the forceps, and 

 sliijhtly warmed, just sufficient to soften the gutta-percha ; the forceps 

 may now be laid aside, or used simply to press the cover home, 

 wanning the slide gently, also the cover ; the perfect contact of the 

 softened ' tissue ' with the cover and slide is easily recognized, and 

 with a little care this can be effected very quickly, and nothing further 

 is necessary. A finishing ring of coloured cement makes a very neat 

 mount, but it is not necessary." 



Mr. F. Kitton, writing* on the above paper, says that he is unable 

 to suggest a remedy. 



The " damping-off " of dry mounts, particularly of diatoms, used 

 to be (some twenty-five years ago) attributed to the imperfect washing 

 of the diatoms : either the acid used in cleaning was not eliminated, or 

 the water used for that purpose was impure ; but preparations which 

 showed no acid reaction, and which had been carefully washed with 

 the purest distilled water obtainable, when dry mounted, still showed 

 the presence of moisture. This was then accounted for (?) by the 

 suggestion that the supposed moisture was really condensation from 

 the asphalt ring supporting the cover ; he therefore mounted somo 

 covers perfectly cleaned (by boiling in acid, washing in distilled 

 water, and afterwards heating them over a Bunsen burner) on somo 

 hard asphalt rings; the slides were heated sufficient to cause the 

 covers to adhere, and when cold the latter were concave, the interior 

 of the cell being nearly exhausted of air. These mounts (about a 

 dozen) were carefully finished, and then left upon the table for several 

 montlis before examination. Some of them showed minute globules 

 on the inner surface of the cover-glass, othei'S minute radiating acicular 

 crystals, and the remainder were perfectly clear. 



Tliis experiment being far from satisfactory, he tried " shellac " 

 as follows : Perforating a hole about ,\ inch in diameter, in a piece of 

 " tliick " thin glass, he covered tlio edges with the lac, and cemented 

 two til in covers to it, aiid with a similar result to the previous experi- 

 ment. He also tried paper cells saturated with " shellac " dissolved 

 ill spirit, or soakeil in paraffin wax, but in no case were they invariably 

 successful. lie has therefore come to the conclusion that the fault 

 rests with the cover itself, and conGrniatory to this opinion is the fact 

 that the covers on balsam {hardened before attaching the cover) sorac- 

 ♦ ' KukI. M.rli..' xxxi. (1S80) p. ."iS'i. 



