MICROSCOPIC PREPARATIONS IN MARINE ZOOLOGY 323 



In a few days, when the exuded balsam is hard and 

 brittle, scrape it off right up to the edge of the cover an 

 old knife made hot in the spirit lamp flame takes the 

 balsam off quickly. When scraped fairly clean dip a rag 

 in methylated spirit and finish cleaning off. Methylated 

 spirit is not a solvent of balsam, but it breaks it up, and 

 allows ready cleaning. If a true solvent is used, such as 

 turpentine, benzole, etc., it will join the balsam under the 

 cover, and spoil the slide. 



A slide left in this way, and neatly labelled, is really 

 finished, as far as utility is concerned, but if it is desired 

 to work a " ring " around the cover place it on the turn 

 table, the edge of the cover exactly coinciding with one 

 of the circles engraved on the brass of the turn table. Re- 

 volve the table a little, to see if the cover is really central 

 and not excentric. Adjust it with precision. Then dip a 

 No. 1. sable brush (camel-hair brushes are no good) into 

 the shellac cement, and, resting the hand holding the brush 

 firmly on the block of the turn table, revolve the disc 

 steadily with the other. Hold the brush vertical, and just 

 allow the point to touch ; the result will be a neat little 

 circle of cement, which should just lap a trifle over the edge 

 of the cover and extend a little bit on to the slip. 



Place the slides away to harden for a day or two ; then 

 replace on the turn table and give a ring of black asphaltum. 

 This is neat and durable. Scarlet, blue, white, and gold 

 rings are sometimes spun around the cover, but, to me at 

 least, this fancy work seems not to enhance the value of 

 the slide, but to detract from it. 



(Do not use the asphaltum without the ring of shellac 

 underlying it, or it will run in under the cover, its solvent 

 being the same as for balsam.) 



Embedding in Celloidin. This presents many advantages 

 when a considerable number of sections of one thing are 

 required, but it does not allow of such thin section 



