526 G. T. HARRIS ON MICROSCOPICAL METHODS 



state the slide is perfectly safe for months, and may be finished 

 at some convenient time subsequently. The finishing consists in 

 ringing with old gold size, coat after coat, with intervals to allow 

 for hardening. 



I have been most desirous of making glycerine jelly mounting 

 a reliable process, owing to its great usefulness in rapidly mount- 

 ing reference slides of leaves and small species of moss. Unfortu- 

 nately I have received several bad shocks in my own work, and 

 in reports from other bryologists, and I must frankly confess to a 

 grave misgiving in asking the Quekett Microscopical Club to 

 accept slides mounted in this medium. Only the fact that I 

 believe some of the principal pitfalls to have been traced and 

 overcome has permitted me to include any at all. Certainly for 

 a long time past now I have been immune from my former 

 perennial crop of lacunae and cavities. In all cases the date of 

 preparation has been marked on the slides, and if they are not an 

 example at least they will be a warning. 



Unless the object is of an appreciable thickness the film of 

 jelly necessary to cover it will not be so thick as to need any 

 support ; but if some species, or portions of large species, are 

 mounted with their capsules the amount of jelly necessary may 

 need some support at the edge to keep the cover-glass even. A 

 convenient way of doing this is to use a ring of silver wire about 

 the diameter of the cover-glass and of a thickness proportioned to 

 the object. Practically a thickness of 23 B.W.G. meets all needs, 

 and I confine myself to this thickness. Silvered wire is easily 

 and quickly prepared by taking copper wire of the desired thick- 

 ness, thoroughly cleaning it from all grease, and immersing it in 

 silver cyanide solution. It can then be kept on a reel, and cut 

 off as required. The ring needs no attaching to the slip, as the 

 gelatine holds it in position ; but it may be slightly flattened by 

 hammering. 



Farrant's medium probably comes next to glycerine jelly in 

 usefulness to the bryologist ; it is very convenient to use, and, of 

 course, allows of great deliberation in arranging the object, re- 

 moving such undesirable matter as can be removed, and it gives 

 good transparency to incrassate cells. For peristomes, which 

 require to be examined by transmitted light, it is excellent, 

 though the fragile endostomes of some species are made too trans- 

 parent by it. 



