1892.] THE MICEOSCOPE. 235 



little fellow, resembling very much a miniature turtle, all of which 

 were literally living oft' of this poor specimen, biting it at pleasure, 

 and seemingly enjoying their feast ; but, alas ! upon examining 

 these very parasites a few days later, who in turn had grown 

 weaker and less active, I found still smaller parasites biting 

 them, verily reminding me of the quaint old saying: 



" Big fleas and little fleas 



Have lesser fleas to bite 'em : 

 The lesser fleas have smaller fleas, 

 And so 'ad infinitum.'" 



Microscopic Low Powers. 



By FREDERICK W. GRIFFIN, Ph.D., 



BRISTOL, ENGLAND. 



The comparatively few microscopists who work with the low- 

 est powers are doubtless fully aware of the advantages of day- 

 light in their use. Lamplight, however, modified by tinted glasses 

 and plane mirror, gives a glare with transparent objects, which 

 tries the eyes and seriously impairs definition. I find, however, 

 the new " Zeltnow cupro-chromic light-filter," which has proved so 

 valuable with high powers, to be equally useful with the lowest. 

 It gives a pale green field, as reposeful to the eye as daylight it- 

 self, while a blaze of light is tempered down to due working 

 pitch. All fine details, as the rings of delicate tracheae, or the 

 markings of a dotted surface, are shown up with the sharpest defi- 

 nition. Of course, color is mainly obliterated in this monochro- 

 matic illumination, the picture being virtually in monotone, like 

 a photograph or engraving. Hence this medium is scarcely suit- 

 able where color is a leading feature of the obi'ect. The solution 

 should be contained in a flat bottle, with clear, polished, parallel 

 sides, as supplied by Baker, and probably other dealers. 



One regrets that the lowest powers (4 in. and under) are so 

 little employed by natural-history observers and amateurs. They 

 aftbrd very useful general views of entire objects, and many 

 striking and beautiful pictures, especially with binocular. This 

 disuse arises from the fact of ordinary microscopes seldom having 

 rackwork sufficiently long to allow of the focusing of very low 

 powers. But a simple adaptation will permit the object to be 

 placed below the stage, so that even a 5-inch objective may be 

 adequately worked on almost any stand. The instrument is like- 

 wise kept steadier, more compact, and less liable to injury than 

 when left out to an extreme length. When there is a " sub- 

 stage " a square plate may be provided with a short tube fitting 

 beneath, so as to fix on the top of it. This may have either 



