12 PROCEEDINGS OF THE ACADEMY OF 



the plate. In use, the hardened metal to be ground true is pressed firmly by 

 the hands of the workman upon the plate, and passed with a sliding motion 

 in various directions over the wheel. The emery wheel touches the highest 

 places, and gradually reduces all to one uniform plane. With this machine 

 straight edges of hardened steel have been produced of such perfection that 

 when pressed together on the edges the one will lift the o her by cohesion, 

 without the intervention of a fluid. 



This machine suggested to me an application of the same principle to the 

 preparation of microscopic objects. For the large plane table with the nar- 

 row opening in the machine, as described, I substitute a small plate of brass 

 or iron, with a circular opening in its centre of about If^'' diam. The emery 

 wheel is supported on a spindle and stand, such as can be purchased at any 

 of the dental depots, and intended for the purpose of rotating emery or corun- 

 dum wheels, &c. The table hinged above the wheel has an adjusting screw 

 to determine the height of its surface plane above the edge of the emery 

 wheel. In use, the specimen, ground and polished on one side, is then 

 mounted with hard balsam on the glass slide upon which it is to remain. It 

 may then he roughly ground down or filed down to any convenient thickness 

 short of that actually needed; then it is laid upon this grinding machine 

 (specimen down), the slide resting on each side of the centre hole in the 

 plate, the specimen touching the revolving emery wheel. Passing it back 

 and forth over the wheel, it is reduced to a plane parallel with the glass upon 

 which it is cemented, and its final thinness regulated by the adjustment of 

 the table. When thin enough for the purpose intended it may be smoothed 

 with a slip of Scotch stone and polished without fear of destroying the uni- 

 formity of thickness obtained by the section-grinding machine. In using the 

 instrument in the preparation of sections of ivory or bone I have found that 

 the grinding should be done with either a dry wheel or one moistened with 

 oil, as water will swell the specimen and crack it loose from its cement. The 

 wheels used bj' me are made of emery and glue, not the shellac corundum 

 wheels sold at the dental depots. It is probable that a circular file, /. e., a 

 steel wheel with teeth on its edge, would do well as a grinding wheel for 

 bones, in place of the emery wheel. 



D. H. C. Wood exhibited slides of mycelium filaments and spores of a fun- 

 gus, which were found disseminated throughout a crust or scab, similar to 

 others expectoi-ated at different times during the past six months by a gentle- 

 man, who had sent the crust to Prof. Leidy. Dr. Wood promised to investi- 

 gate the subject further, but up to the present time could not speak precisely 

 as to the specific form. The filaments resembled those found by Virchow and 

 others in the lungs, and called by them aspergillus pulmonum. 



June 21st. 



Director S. W. Mitchell, M. D., in the Chair, 



Eight members preseat. 



Dr. W. W. Keen read a paper on the stibject, " Is Atropia an 

 Antidote to Hydrocyanic Acid?" 



Dr. Mitchell desired to know whether the quantities used were at all com- 

 parable to those of Pryer. 



Dr. Keen replied that this was the point most difficult to determine, but 

 having found by experiment that two minims of the oflicinal hydrocyanic acid 

 of our Pharmacopoeia was a lethal dose for rabbits, he had then sought to 

 make the quantities accord with those of Pryer. 



