ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 255 



might possibly notch the knife. When in use, the glass plate is laid on 

 the upper face of the block and is fastened down with screws. It is then 

 smeared with a fine emery paper moistened with distilled water ; or with 

 Vienna chalk paper moistened with distilled water ; or with iron oxide. 

 The knife is then drawn rather frequently over the plate (60 or 70 times), 

 and the edge is held forward, in such a position that it is perpendicular 

 to the direction of movement. The knife-edge as it appears under a 

 magnification of 100 diameters is shown in fig. 48. A special facet of 

 20° to 25° is ground on the knife by placing the back of the knife in a 

 laterally-open iron tube, and clamping it with screws (fig. 41). From the 

 diameter d of the tube and the breadth a of the knife the angle (a x + a 2 ) 

 can be calculated. Thus 



— = tan a, + tan a 



(fig. 41). The facet, which has been roughly fashioned with emery, is per- 

 fected with Vienna chalk, the teeth on the edge now becoming very fine 

 (fig. 44) under the same magnification as before. The iron-oxide is only 

 used for whetting that side of the facet which glides, when in action, on 

 the paraffin or celloidin. 



Rotatory Method in Microscopy.* — H. Lebrun, after three years' 

 experience of his method of diskal arrangement,! sees his way to several 

 improvements, the first of which is concerned with the microtome. It 

 was found that in cutting very thin sections tremor of the machine 

 caused much irregularity in the sections themselves. This difficulty the 

 author remedies by attaching the knife-carrier to parts of the microtome 

 not liable to agitation. The paraffin block, instead of being truly rect- 

 angular, is now made with sloping slides according to the size of the 

 disk on which the serial sections are to be received. Full directions 

 are given for accurately obtaining the proper shape of block. There 

 are several other improvements in the mechanism and manipulation of 

 the microtome. As above-mentioned, the object-carrier is disc-shaped, 

 the rectangular form being abandoned. An ingenious combination of 

 hand and screw-work brings every part of the object, in spiral fashion, 

 successively under the objective. This arrangement is also particularly- 

 convenient in the case of such an object as a tapeworm. The author 

 recommends his method as tending to great economy both in materials 

 and in time. His ideas have been satisfactorily worked out for him by 

 the firm of Seibert, of Wetzlar. 



Simple Method of Paraffin Imbedding in Vacuo.! — W. Berg 

 describes a method which is applicable to any ordinary paraffin oven. 

 The paraffin is contained in a glass flask, firmly stoppered, which com- 

 municates by means of stout rubber tubing with an ordinary water suction 

 apparatus. The rubber tube passes through the hole in the top of the 

 oven, which normally holds a thermometer. It is advisable that the 

 paraffin should fill only the lowest portion of the flask, as it foams some- 

 what, when the exhausting process is commenced. This procedure does 

 not interfere with the ordinary use of the oven. 



* Zeitschr. wiss. Mikrosk., xxvi. (1909) pp. 223-41 (13 figs.). 



t See this Journal, 1906, p. 725. 



J Zeitschr. wiss. Mikrosk., xxvi. (1909) pp. 209-10. 



