MICROSCOPIC OBJECTS. 



23 



with diffused light, yet its color, or the 

 strong contrast of one part with another, 

 may be such as to render a photograph of it 

 quite impossible. Take, for instance, an 

 object mentioned in our first lesson, the 

 tongue or proboscis of a fly ; satisfactory 

 photographs of this object are not common, 

 simply because they have been taken from 

 the specimens usually met with in collec- 

 tions which have been prepared to give the 

 best effect when seen through the micro- 

 scope, where the strong contrast in depth 

 of color between the lobes of the ligula 

 and the thick portion of the maxillae and 

 maxillary palpi is no defect, but positively 

 an advantage. When such a specimen is 

 photographed, its unfitness is clearly seen ; 

 the thin, transparent lobes are usually much 

 over-exposed long before the darker parts 

 of the ligula have received their proper 

 amount of light ; in short, no exposure will 

 suit this object as a whole. It is true a 

 sort of makeshift may be employed, and 

 fair results gained, by shading the trans- 

 parent parts during exposure, keeping the 

 shade in gentle motion all the time, during 

 half or three fourths of the exposure, when 

 the whole may be exposed. It is far more 

 satisfactory, however, either to select one of 

 the tongues from a large number, or pre- 

 pare one specially, so as to subdue these 

 undesirable contrasts, and bring the whole 

 object more into harmony as regards den- 

 sity. 



The beginner in photo- micrography is 

 strongly advised to make his own micro- 

 fcupic preparations. A microsiope can 

 never be much more than a pleasant toy 

 if its possessor rely whcjlly on purchased 

 slides. To own even a moderate collec- 

 tion of slides prepared by the professional 

 mounter will cost a large sum of money, 

 and when these have been examined a few 

 times, their interest is gone, and the micro- 

 scope is laid aside for want of objects to ex- 

 amine. But when the student prepares his 

 own objects, his microscope becomes to him 

 a continual source of pleasure and instruc- 

 tion. His slides, in the majority of cases, 

 may not be equal to those professionally 

 prepared, and they will certainly lack that 



exquisite finish which constant practice in 

 their preparation alone can give; but for 

 the purpose of study, and especially for 

 photo micrographv, they may be equal to, 

 or even better than, anything that can be 

 purchased from the optician. Then, with 

 practice, the student will so far improve 

 that he will find his own preparations so 

 much better for his special purpose, that he 

 will rarely visit the optician's shop for 

 slides, unless it be to purchase some object 

 that cannot be produced elsewhere, or one 

 which may be beyond his own powers to 

 prepare. That there are such objects, it 

 cannot be denied ; and we may perhaps 

 place anatomical preparations in the list of 

 objects better left to the experience and 

 skill of the professional preparer. As the 

 student will not require his objects to be 

 mounted in fancy style, he may prepare 

 slides of such diatoms as he can find in his 

 walks, or obtain by exchange, small as 

 these objects are, purchasing only the rarer 

 forms, or such as are prepared especiilly as 

 test-objects. Practice in preparing and 

 photographing minute objects, like diatoms, 

 is not only desirable, but necessary, to give 

 the beginner complete command over his 

 microscope and camera. 



The apparatus required in the prepara- 

 tion of microscopic objects is neither cum- 

 brous nor costly. The following list in- 

 cludes most of what the beginner will 

 require: A spirit lamp; needles mounted 

 in wooden handles; glass slides, 3 in. by 

 I m. (these should be of plate-glass with 

 ground edges) ; circles and squares of thin 

 cover glass, the thinner the better; solution 

 of potash, commonly called liquor potas- 

 sos; methylated spii its; spirits of turpen- 

 tine; some pure benzole, not benzoline; 

 nitric, sulphuric, and hydrochloric acids; 

 chlorate of potash; a bottle of balsam, 

 or balsam and benzole; glycerine; gela- 

 tine; fine and coarse emeiy ; a glass plate 

 (,^'<&[tx2.\Ay plate glass) about a foot square, 

 and one of cast iion the same size, for grind- 

 ing down sections of horn, bone, or rocks ; 

 a pair of scissors ; a sharp knife ; a pair of 

 forceps ; and a d.izen brass clips for holding 

 the covers on the slides, will also be required. 



