ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



619 



object ; the second, with a black ring, intercepts the rajs of medium 

 obliquity, which cause a coloured veil in strong objectives and in im- 

 mersions. It is possible also to use a star diaphragm with a centre 

 tinted complementarily to the filter, the result being double colorations. 

 The other conditions for producing chromoscopic images are : (1) use 

 of daylight or of a light-source of large extent ; (2) use, by preference, 

 of a condenser of large aperture, and, in all cases, joining the object- 

 slide to the condenser by a drop of liquid. 



As illumination by the short waves affords the maximum of resolu- 

 tion, it is advantageous to employ the violet filter for direct observation : 

 the red, inactinic, chromoscopic filter is favourable for photography. 

 To appreciate the services which chromoscopy can render, the author 

 recommends the observer to try the effect on fresh blood (leucocytes 

 with their nuclei coloured in contrast with the red corpuscles), infusoria, 

 aud vegetable sections. 



Adaptable Eye-shade for Microscopic Use.*— S. G-. Shattock draws 

 attention to the advantage which is derived from cutting off the access 



(Mill in I i nil i mil minimum) 



I— -/A 



Fig. 65. 



of direct light to the eye above the ocular. In working in a darkened 

 room with a hooded lamp this drawback does not of course arise. But 

 when daylight is used the admission of light to the eye above the ocular 

 is a distinct hindrance to the study of fine detail. The difference ran 

 be at once brought home by temporarily shading the eye with the hand 

 so as to improvise a dark chamber above the ocular. The ability to see 

 more minute details with an eye-shade and a consciousness of diminished 

 strain will become so apparent, that once used, it is certain the device will 

 be afterward invariably resorted to for any prolonged microscopic study. 

 Mansell J. Swift, who makes the device, told the inventor that binocular 

 Microscopes were occasionally fitted with shades, but these (as in the 



Brit. Med. Journ., ii. (1915) p. 504 (1 fig.). 



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