24 



HOW TO PHOTOGRAPH 



It is best to keep the balsam in a bottle 

 fitted with a wooden stopper, through which 

 a glass rod may be passed. The end of 

 the rod may be kept above the balsam 

 when not in use. When it is required to 

 take some balsam out, the rod can easily be 

 pushed down until it justs dips below the 

 surface, and a small quantity taken ont 

 without soiling the neck of the jar. Corks 

 should not be used, as they are apt to stick 

 fast, and, by crumbling away, fill the bal- 

 sam with small fragments which are difficult 

 to remove. By keeping the glass rod al- 

 ways in the bottle, it will remain clean, 

 which would not be the case where it kept 

 elsewhere; and the learner will soon find 

 that cleanliness is absolutely necessary in 

 microscopic work. 



Newly purchased slides and covers are al- 

 ways dirty. Water will not always effectu- 

 ally cleanse them ; they should therefore be 

 washed in a solution of caustic potash, am- 

 monia or soda. This will free them from 

 impurities ; but the slides should afterwards 

 be well rinsed m pure water, or some of 

 the alkali will remain on the glass, and 

 prove as great a hindrance as the dirt. 



Microscopic objects are mounted in tliree 

 different ways : l. Dry. 2. In a gum, such 

 as balsam or dammar. 3. In some fluid 

 such as water, glycerine, or alcohol. Dry- 

 mounted objects being usually opaque, are 

 not well suited for photography, unless the 

 operator has more than common dexterity 

 in the management of reflected light. In 

 the cape of very transparent objects, how- 

 ever, such as diatoms, dry mountmg is far 

 the best, as the use of balsam or glycerine 

 does much to obliterate fine mai kings, on 

 which the interest of the object, perhaps, 

 entirely depei ds. Balsam or dammar will 

 most generally be used as the mounting 

 medium, as these gums render an object 

 mounted in them more transparent, and 

 can be used in mo?t cases where they exer- 

 cise no solvent action on the preparation, 

 infect preparations, vegetable tissues, rock 

 sections, crystals of various salts, are, as a 

 rule, photographed to best advantage when 

 mounted in balsam. 



As insect preparations are of perhaps 



more general insterest than any other, and 

 are more easily photographed, we shall 

 treat of preparing these objects for photog- 

 raphy in our next lesson. 



Lesson IX.— Preparing Entomolog- 

 ical Slides. 



A glance at the catalogues of the profes- 

 sional prepaiers will show how popular are 

 insect preparations. Nor is this surprising. 



The marvellous beauty of form, the gor- 

 geous colors, the elaborate workmanship 

 displayed in the construction of their vari- 

 ous organs, together with the minute size of 

 many of the insect tribe, all render them fit 

 objects for microscopic study. Many of 

 their beauties are apparent to the unaided 

 eye, but under the microscope they are in- 

 creased tenfold ; while others alone reveal 

 themselves to the scrutiny of the magic 

 tube. But for it, the delicate mosaic of the 

 butterfly's wing, the mysteries of the gem- 

 spangled elytra of the diamond beetle, the 

 myriad-facetted eye common to the whole 

 insect world, and all the wonders of their 

 internal structure, would remain hidden to 

 us. 



As insects vary so much in size, colors, 

 and texture, the modes of preparing them 

 for photography must also vary to suit the 

 subject under treatment. 



I. Opaque Mounting. — This method is 

 alone available in some cases, as the appli- 

 cation of balsam or any medium would not 

 only diminish the beauty of the specimen, 

 but often prove destructive in effect. Such 

 objects as scales, such as those of butterflies, 

 the Podura and Lepisma, as well as some 

 wings which are very transparent, as well 

 as small insects like the Tingis and Thi ips, 

 which can be successfully photographed by 

 reflected light, should be mounted dry. In 

 the case of small flat objects, as scales, no 

 cell will be required ; ail that is necessary 

 is to place the scale in position on the slide, 

 and cement a thin cover over it. Larger 

 objects will require a cell, which, for pho- 

 tography, had better be of glass. Glass 

 celis are sold at a cheap rate, look well, 

 and have the advantage of allowing light to 

 pass through their sides, which is often de- 



