June 4, 1897.] 



SCIENCE. 



865 



beiDg returned to position to begin cutting 

 and after the object has passed under tlie 

 knife. 



" Ease with which feed screw may be re- 

 turned when fed up to its full limit." 



III. A NEW FOKM OF MICROTOME KNIFE. 



To satisfactorily sharpen a knife for fine 

 section- cutting is a diffiulty, which we all 

 have learned to estimate as serious. The 

 valuable article bj' Moll on sharpening 

 in the Zeitschrift fiir Wmenschaftliche Mikro- 

 skopie in 1S92 (Bd. IX, p. 455) called my 

 attention to various possibilities, and at my 

 request Dr. F. S. DeLue tested a number of 

 methods. These tests resulted in the adop- 

 tion of plate glass and diamontine powder 

 mixed with water as the best means of se- 



matic wheel ' microtome. In both knives the 

 essential features are the same, the propor- 

 tions only being different. The larger knife 

 is 330 mm. long ; its cutting edge is 185 

 mm. long, and it is 12 mm. thick at the 

 back. The smaller knife is 160 mm. long; 

 its cutting edge 85 mm. long, and it is 10 

 mm. thick at the back. These knives have 

 the handles of the same cross section as the 

 blade ; they are alike on both sides, being 

 slightlj^ concaved. A knife of this pattern 

 can be laid upon a glass plate, upon which 

 a little water with diamontine has been 

 rubbed; the knife rests upon its cutting 

 edge and upon its back edge, and may be 

 perfectly sharpened without any special 

 technical skill bj^ simply passing the blade 

 to and fro, resting alteriiatelj'^ first on one 



curing a satisfactory cutting edge. Plate 

 glass seems to have been used from time to 

 time, and is especially recommended by 

 Moll. The use of diamontine powder was 

 suggested by Dr. Lotze (Johns Hopkins 

 Hospital Bull., Dec, 1894). 



Having at command a satisfactory 

 method of sharpening, it soon became evi- 

 dent that the knives should have a form to 

 which that method could be applied con- 

 veniently. It was necessary that the knife 

 should be : 1, rigid ; 2, slightly hollowed on 

 both sides ; 3, of such shape that it could 

 rest its whole length on a plane surface ; 4, 

 that there should be no edge to be sharp- 

 ened, except such as could be used for actual 

 cutting. These four requirements are met 

 by the pattern illustrated in Fig. 5, already 

 made in two sizes, the larger being intended 

 for the ' PreciS('o)i,' the smaller for the ' Auto- 



side, then on the other, until the entire edge 

 is completely polished. 



The knife is then removed, thoroughly 

 cleaned, the glass plate also cleaned and the 

 edge finished bj^ polishing on the glass plate 

 with water only. The glass plate by itself 

 will remove any wire edge which may be 

 left by the diamontine powder. 



It often requires considerable time to get 

 the first edge on a new knife, for the knives 

 as furnished by the manufacturers ai-e never 

 quite straight, but after the edge has been 

 once obtained it is easily kept in condition, 

 provided that it is not allowed to become 

 nicked or dented through careless handling. 



There is one precaution in the use of this 

 method of sharpening which cannot be 

 taken too conscientiously, namely, to keep 

 the glass plate while in use absolutely free 

 from dust and dirt of every description ; 



