The Microscope. 75 



resolution of No. 15 by central and No. 20 by oblique light, 

 with only a slight darkening of the secondary spectrum in the 

 latter condition, furnishes abundant proof. This objective, 

 which is a new one, not yet down on their list, has a balsam 

 angle of 105°, and working distance of a little more than one- 

 thirtieth (correctly, 0.037) of an inch. The single fluid used 

 with it, is one which has been devised by Prof. H. L. Smith, 

 having an index as nearly coincident with that of the front lens 

 as anything yet devised. 



Thus, it will readily be seen that by doing away with one 

 of the fluids, and yet not impairing the performance of the ob- 

 jective, its value is greatly increased as a convenient working 

 lens. 



BULLOCH'S COMBINATION MICROTOME. 



THIS microtome which has lately been constructed by W. H. 

 Bulloch, is a combination of the best points of the German 

 and French with some of his own improvements. The illustra- 

 tion will, to a certain extent, give a general idea of the con- 

 struction. The main slide for the knife carrier is 10| inches 

 long, height to cutting edge of knife, 5-J inches. The knife car- 

 rier is made with eight ivory bearing surfaces, four on each side, 

 which allows of a smooth and easy running surface, and which 

 does not require to be lubricated, only to be kept clean. At 

 each end of the main slide there is a stop with rubber cushions, 

 to prevent the carrier passing over the end. The upper surface 

 of the knife carrier is made adjustable so the knife can be made 

 to cut at whatever inclination is found best. The knife can also 

 be placed at any angle for cutting or adjusted to cut at right 

 angles for cutting sections in ribbons. Some authorities claim for 

 cutting fibrous tissue or hard sections, a long sliding cut is pref- 

 erable, whereas for cellular or soft tissue a cut square with the 

 material is best. The screw for elevating the slide and holder 

 is graduated to tbi mm, about sooo of an inch ; and with spring 

 click for registering or counting thickness of sections. The 

 spring click can be turned aside when not required. The holder 

 for material has universal motion, so that the specimen can be 

 adjusted to cut at any plane. Each motion is independent of 

 the other ; and are so combined that the specimen is not raised 



