240 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



cated metal prism, is connected with the lower face of the 

 glass slide by interposition of a drop of oil of cloves. Hays 

 transmitted through this prism will, of course, not be received 

 into any dry objective, or any immersion one of less than 90 

 balsam ano-le when transmitted through balsam-mounted ob- 



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jects. With those objectives, however, that will admit such 

 rays (giving a bright field) and are properly corrected, the 

 Amphiplcura pcllucida is readily resolved in balsam. In the 

 same journal is a note on a new "Paraboloid Illuminator" for 

 use beneath the microscope stage, by James Edmunds, M.D. 

 It is a modification of the well-known Wenham parabolic illu- 

 minator, much smaller, and made with great care being, in 

 fact, a paraboloid lens, of glass, of low refractive index, care- 

 fully cut off at a point about one twelfth of an inch below 

 its latus rectum. The truncated surface is connected with the 

 under surface of the slide by glycerin, and suitable stops, 

 etc., are applied under the lens. 



HISTOLOGY. 



Dr. J. G. Richardson, of Philadelphia, having obtained spec- 

 imens of blood from the several individuals of different parts 

 of the world who went to the Centennial Exposition last au- 

 tumn, after measuring carefully every isolated circular red 

 disk, cautiously avoiding those that manifested even slight 



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departures towards an oval form, arrived at the following 

 results, which we condense from the tabular view given in 

 the American Naturalist, March, 187*7 : 1400 corpuscles were 

 separately measured ; the average size was , d fa 4 (0.007878 

 mm.), the maximum was t> t Vt, and the minimum 4-0V0 of an 

 inch. Of these, 1 158, or 83 per cent., measured between j 4 T 48 

 and tjuVo or> an i ncn , a difference of size scarcely discernible 

 with a power of 200 diameters ; about eight per cent, were 

 less than -345-5-, and nine per cent, more than ^nnnr f an inch 

 in diameter ; the total number ^nn> of an inch across was six, 

 or less than one half of one per cent. ; and the total number 

 ttytt of an inch in diameter was ten, or less than one per cent. 

 Ilerr Ebner, in a memoir on the histology of the hair, pre- 

 sented to the Academy of Sciences, Vienna, July 12, states 

 that the inner root sheath is essential for hair-formation ; and 

 1 hough broken through by the hair, it grows during the whole 

 hair-vegetation, in the lower part of the follicle, with even 



