298 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



type-series of sections of sucli objects as, when cut into thin sections, would 

 occupy a very large number of slides of the ordinary form, — such as the 

 earthworm, leech, fluke, Amphioxus, chick, mammalian embryos, and the 

 like : but besides its use for demonstration purposes it is also claimed to 

 be of the greatest service in investigation. 



The sections are mounted on circular discs of glass a, figs. 46 and 47, 9 in. 

 to 11 in. in diameter, with a circular aperture of 8 or 4 inches in the centre. 

 The method of procedure is as follows : — The glass disc after being care- 

 fully cleaned is smeared over thinly with a very thick solution of shellac 

 in creosote. It is then laid on a sheet of white paper on which concentric 

 circles a quarter of an inch or thereabouts apart, from the size of the disc 

 downwards, have been ruled. The sections, cut by an automatic microtome, 

 are laid round the outer edge of the disc in concentric circles, their position 

 being regulated by the concentric lines on the paper. To facilitate the 

 arrangement of the section it is advisable in paring down the block of 

 parafBn to leave the sides not quite parallel, but inclined to one another at 



Fig. 46. 



Fig. 47. 



about the angle between two radii of the disc separated near the circum- 

 ference by th«i thickness of the Vdock ; by this means is produced a ribbon of 

 sections which is not straight but curved, with about the curvature re- 

 quired. The disc is then warmed in the usual way to dry the creos )te and 

 melt the parafl&n, and is flooded with turpentine to dissolve out the latter : 

 balsam is poured on and the sections are covered with oblong strips of thin 

 cover-glass. In this way may be regularly arranged on the disc a series 

 containing thousands of sections. 



The apparatus for enabling the series to be examined is a brass revolving 



