THE MICROSCOPE. 17 



cap A and partly by the silver cup or speculum I. In 

 front of the lens is the speculum I, a quarter of an inch 

 thick at its edge, having a focus of half an inch, and in 

 front of this there is a disc of metal c, three-eighths in 

 diameter, connected by a wire with the small knob D ; upon 

 this disc the injected portion is fastened, and is covered 

 over with some kind of varnish which has dried of a hemi- 

 spherical figure. Between this knob and the inside and out- 

 side of the tube there are two slips of thin brass, which 

 act as springs to keep the wire and disc steady. When 

 the knob is moved, the injected object is carried to or from 

 the lens, so as to be in its focus, and to be seen distinctly, 

 whilst the condensing lens B serves to concentrate the light 

 on the speculum. To the lower part of the tube a handle 

 of ebony, about three inches in length, is attached by a 

 brass ferrule and two screws. The use of this instrument is 

 obvious; it is held in the hand in such a position, that the 

 rays of light, from a lamp or white cloud, may fall on the 

 condenser B, and by it be concentrated on the speculum I, 

 which again further condenses them upon the object on the 

 disc C; the object, so illuminated, can readily be adjusted by 

 the little knob D, so as to be in the focus of the small 

 magnifier at A. 



The injected preparations in these twelve microscopes, now 

 nearly a century old, are remarkably beautiful, and the only 

 injury which they have sustained, is that of the cracking 

 of the varnish. Lieberkuhn's principal researches were 

 confined to the minute structure of the mucous membrane 

 of the alimentary canal ; and for the investigation of these 

 opaque parts, he is said to have invented the silver speculum 

 bearing his name, although, from a description and figure 

 in the works of Leeuwenhoek,* one would be inclined to 

 suppose that that illustrious man was cognizant of its prin- 

 ciples and use. 



The other microscope which Lieberkuhn used for the ex- 

 amination of the mucous membranes, and the circulation of the 

 blood and chyle in the mesentery of small animals, is repre- 

 * Vol. ii. p. 280, Works by Hoole. 

 2 



