ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 967 



The objects examined were : fresh human blood, epithelium from 

 the mouth, and saliva-corpuscles, numerous preparations (stained 

 with colouring matters of all kinds) of muscle, nerves, epithelium, 

 bones, skin, embryos, bacteria, " test objects " {Pleurosigma angu- 

 latmn). Especially surprising was the faultless image of the red 

 blood-corpuscles, an object which has hitherto for the most part 

 withstood artificial ilhimination. Even with the weaker incandescent 

 lamps, the faint htemoglobin colour of the corpuscles showed a clear- 

 ness beyond expectation. 



A few more intense pigments, on the other hand, were considerably 

 altered : in daylight saturated blue imbibitions, prepared with indigo- 

 carmine, borax, and oxalic acid, were a dingy reddish-violet, with 

 every kind of electric illumination, whilst objects coloured with 

 anilin-blue were a more intense blue, and, when in thick sections, 

 blackish blue. All coloured green with indigo and picric acid were 

 of a decided saturated green. 



A Crompton arc-lamp, of about 3000 candle-power, was found 

 quite as advantageous as the incandescent lamps. The light, 

 diminished (by about 15 per cent.) by an opal glass shade, and 

 placed at a distance of 2 • 1 m. (in a horizontal direction) from the 

 mirror of the Microscope, and raised 1 • 1 m. above it, was found the 

 most convenient, whilst the plane mirror of Abbe's illuminating 

 apparatus was adjusted, not on the brightest point, but on an adjoining 

 portion of the globe. In this case the ground glass under the object 

 was indispensable, and may always be reckoned an advantage. Where 

 exceptionally such great brightness is requisite this illumination is to 

 be recommended. 



In order to see how far the excess of light promised advantage, 

 the shade was removed, and the mirror adjusted on the carbons. 

 Instead of the ground glass, which produced a field of view full of 

 spots, a small piece of oiled tissue-paper was placed over the upper 

 surface of the Abbe illuminating lens, and the smaller diaphragm 

 inserted. An object, consisting of mouth-epithelium and saliva- 

 corpuscles, observed with this illumination and Zeiss's oil-immersion 

 1/18 and a strong eye-piece, has perhaps given the most perfect 

 microscopic image that has yet been seen. It was, indeed, attempted 

 to obtain the same with direct sunlight, but with only partial success, 

 as it was necessary to dim the sunlight by ammonio-oxide of copper. 



Further to increase the illumination by a parabolic reflector appears 

 impracticable, as the heat, which had never before been troublesome, 

 became unbearable, even at a distance of several metres. 



The whiteness of the electric light, resembling in this respect 

 daylight, especially adapts it to the observation of such objects as are 

 recognizable essentially by differences of colour. Fresh preparations 

 of pathologically changed organs (cancerous and cirrhous liver), and 

 fine shades of skin pigments of animals, were perfectly demonstrated 

 by the incandescent lamps, and whilst enjoying the advantage of these 

 almost non-heating lamps, by which the observer may be surrounded 

 on all sides, there is no difficulty in undertaking the finest zootomical 



