582 SUMMARY OF CURRENT RESEARCHES RELATING TO 



completely fills the cell. In the former case it is evident that the 

 balsam is finding its way into the cell, though slowly, and if it is thin 

 enough to retain its soft condition for a few days, the bubbles will 

 probably disappear ; but when they completely fill the cell it is a 

 sign that the balsam cannot find entrance, and the object can then 

 only be cleared by again soaking it in the fluid solvent. Among the 

 objects most liable to this inconvenience may be mentioned sections 

 of some wood, also such Bryozoa as some of the common Catenicellce, 

 the avicularian processes of which usually contain perfectly closed-in 

 chambers. In the closed gonothecse of some of the most delicate 

 hydroids the same cause is followed by different results — the escape 

 of the fluid and the inability of the balsam to enter, causing the 

 collapse of the thin chitinous investment, instead of the formation of 

 a vacuum-bubble, as is the case where the wall of the closed cavity is 

 strong enough to resist the pressure of the balsam. Precisely the 

 same phenomenon is observed when delicate vegetable tissues are 

 placed in glycerine, and the means used to prevent it, viz. thickening 

 the medium very gradually, suggested to me the idea of applying the 

 same principle to balsam mounts. 



An easy method of doing this is to place the object in turpentine 

 on the slide under a large cover-glass, and with a glass-rod, deposit 

 round the margin an embankment of soft balsam, then lay the slide 

 aside till the balsam and turpentine are thoroughly mixed, which will 

 be a slow and gradual process. It is not advisable to use carbolic 

 acid for this work, at least if there be any considerable depth between 

 the cover and the slide, as the mixture of acid and balsam assumes a 

 rather deep colour. A slight modification of this plan may be used 

 with advantage to prevent delay in the drying of the slide, as follows : 

 ■ — Place the object (saturated with carbolic acid) in the middle of the 

 slide, and make a little embankment of balsam at some distance all 

 round it, then fill the space within the balsam with a pool of the acid, 

 and place the slide under the cover till the acid and the balsam are 

 sufficiently mixed (ten minutes or a quarter of an hour), then drop 

 fresh balsam on the object and cover as usual. Turpentine is not 

 suitable for this purpose, as it runs all over the slide." 



Mounting Moist Objects in Balsam.*— Dr. Johnson (of Victoria) 

 some years ago recommended as a means to mount Sertularians, 

 Bryozoa, &c, that the objects should be boiled in water till all the air 

 is removed, then drained, placed for a few hours in carbolic acid, and 

 thence transferred to the slide and mounted in balsam. It will be 

 found, however, writes Mr. W. M. Bale, " that the water contained 

 in the interior of the specimens being taken up by the acid will, 

 unless a large quantity of the latter be employed, or the objects be 

 placed in two successive baths of it, be sufficient to cause a cloudiness 

 in the balsam. Moreover, it is frequently undesirable to lose time 

 by putting the object aside till the water and acid have completely 

 mixed ; and to remedy these inconveniences, the object, after removal 

 from the water, should be placed in methylated spirit, which will 



* Joum, Micr. Soc. Victoria, i. (1882) pp. 104-5. 



