ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



737 



by the bar a, constitute tlie automatic sliarpener. Their surfaces are 

 covered with leather, which is supplied with tripoli or rouge fx'om 

 time to time as needed. These wheels are set at a slight angle with 

 the radius of the knife, as shown in elevation, and while the knife may 

 have a very rapid revolution, the wheels move but slowly. When not 



Fig. 177. 



needed the bar a and wheels may be turned up out of the way. After 

 the specimen is imbedded by dipping or casting, one side is cut flat, 

 the plate U is heated and held in contact with the flattened surface a 

 short time, and the stem put into the carrier-arm and turned. If the 

 specimen is to be kept in book form, put a piece of tissue-paper on the 

 lower side of the cast and cut to it. 



Notes on Section-cutting.* — Mr. E. L. Mark, of the Museum of 

 Comparative Zoology at Cambridge, Mass., U.S.A., writes as 

 follows : — 



" My only apology for the present communication is the hope 

 that it may prove a saving of time to those who have encountered 

 the difficulties of cutting eggs, which are composed largely of yolk- 

 corpuscles liable to crumble in the ordinary paraffin method. The 

 difficulty I have experienced lies not alone in the impossibility of 

 making sections — even from eggs very thoroughly permeated by the 

 paraffin — which will not crumble during the removal to the prepared 

 slide, but also in the fact that sections successfully transferred to the 

 slide are liable to have portions of the yolk-granules loosened and 

 floated over other portions of the section during the removal of the 

 paraffin. While by the ordinary methods of mounting (Giesbrecht, 

 8challibaum) those elements of the section which lie on its under side, 

 and therefore come in immediate contact with the fixative, are safely 

 held in place, it may happen that many from the upper surface are 

 kx^sened and washed away, because the fixative docs not penetrate 

 the whole thickness of the section. 



* Amer. Natural., xix. (1885) pp. 628-31. 



