1884.] 



MICROSCOPICAL JOURNAL. 



73 



ing away all the acid, pour on enough 

 strong ammonia to cover the sedi- 

 ment. Let it remain two or three 

 minutes, wash again, and then sepa- 

 rate the forms by gravity as before 

 described, using test-tubes instead of 

 bottles. 



If these operations are conducted 

 as we have described them, a clean 

 collection of the beautiful skeletons 

 will be obtained, from which fine 

 mounts can be made. The methods 

 of mounting will be given in the 

 course of the articles on Microscopi- 

 cal Technic. 



The method above described is in- 

 tended for those who wish to obtain 

 only the finest and most striking 

 forms. For the student of the radio- 

 laria who would desire to keep the 

 more delicate forms as well as the 

 others, the treatment should be some- 

 what modified, and the disintegration 

 of the rock would be more gradually 

 effected. 



Microscopical Technic. 



III. MOUNTING OBJECTS DRY. 



By far the greater number of ob- 

 jects that are mounted dry are best 

 examined by light condensed upon 

 them from above. Occasionally very 

 thin and transparent specimens, such 

 as diatoms, foraminifera and radiola- 

 ria, spicules, thin sections of plant 

 stems, cuticles, leaves, etc., are 

 mounted dry for transrnitted light. 

 A thin section of elder pith, for ex- j 

 ample, mounted dry and illuminated 

 with a paraboloid, makes a fine ob- 

 ject ; but generally such specimens 

 are seen better when immersed in a 

 medium like Canada balsam. | 



We shall select for description \ 

 such specimens as seem best calcu- : 

 lated to cover the whole field of dry i 

 mounting. 1 



Dry 'Transparent Mounting. — In 

 describing this method of mounting, 

 perhaps we can do no better than to 

 follow the process of mounting dia- 

 toms. The glass slips and covers 



should be selected and cleaned, and 

 the mounting apparatus placed near 

 at hand. Tlien proceed to prepare 

 the cells, as follows : Put a slide on 

 the turn-table, and make a ring of 

 shellac in alcohol upon it, just large 

 enough to support a i-inch cover- 

 glass. Prepare a number of slides 

 in this way, and set them aside for 

 the shellac to harden. In twenty- 

 four hours they are ready for use ; 

 but if there is not time to wait for 

 spontaneous drying, heating over the 

 spirit-lamp will harden the shellac in 

 a few moments. 



When the cells are ready the dia- 

 toms may be prepared on the cover- 

 glass, for it is better to mount such 

 minute specimens upon the cover- 

 glass than upon the slide. The rea- 

 son for this is that in case it should 

 be desired to examine them with a 

 lens of high power and short working 

 distance, they will be nearer to the 

 lens and more readily focussed upon 

 if attached to the under side of the 

 cover-glass than if on the slide itself. 

 Moreover, there are optical reasons 

 which make it advantageous to mount 

 the finer diatoms in this way. 



Assuming that the latter are prop- 

 erly cleaned, and preserved in a mix- 

 ture of equal parts of alcohol and 

 water, it is necessary to dry a very 

 thin and evenly distributed layer upon 

 the cover-glass. The simplest way 

 to do this is to support the cover up- 

 on a thin piece of metal, and heat it 

 with the spirit-lamp until all organic 

 matter is burnt away. An excellent 

 support can be cut from a piece of 

 ferrotype metal, such as is used by 

 photographers. Take an old ferro- 

 type picture and cut out a narrow 

 strip, about j^ of an inch wide, with 

 an enlarged rounded end a trifle more 

 than half an inch in diameter to sup- 

 port the cover-glass. Select a bottle 

 of the proper height, load it with 

 shot or sand, and thrust the small 

 end of the support into the cork of 

 the bottle. Put the cover-glass on 

 the support, dip up a drop or so of 

 the fluid containing the diatoms, and 



