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flDicro0copicaI ZTecbniquc 



Compiled by W.H.B. 



The Best Method of Sharpening a Microtome Knife.*— Dr. 



Lotsy thinks that Moll's method of sharpening microtome knives 

 is the best, as " it allows one to put the knife in good shape inside 

 of a few minutes for any section he wants to cut. Before using 

 this method, any concavity of the knife-blade must first be taken 

 away. Dr. Moll uses a plate of polished glass, which is fixed in a 

 piece of wood, and two different powders, viz. — Vienna chalk and 

 diamantine. A paste is made of one of these powders and put 

 upon the glass ; then the knife is simply moved backwards and 

 forwards upon the glass over the paste. By means of the Vienna 

 chalk you can polish your knife in a very few minutes. The dia- 

 mantine allows you to put a sharp edge on it, but does not give a 

 polished surface, but rather a rough one. Now, when you have a 

 knife which is highly polished, you can cut a section of, say, 5^ 

 perfectly well ; but if you try to cut with it a section of i to 2^, 

 you will not succeed at all ; your sections will become compressed 

 and wrinkled, and you can do nothing with them. On the other 

 hand, if you try to cut a section of 5^ with a knife having a rough 

 surface, your section rolls up. This rolling up of a section has 

 been represented to be a fault in the paraffin, but that is not the 

 case. We must adapt the knife to every thickness of section we 

 wish to cut. Starting out with a certain knife, if your section 

 curls up, the proper thing to do is to polish your knife with Vienna 

 chalk, and your section for that thickness will not curl up. any 

 more. If your section becomes too much compressed, your knife 

 should be rubbed over the diamantine and the polished surface 

 taken away, when the sections will be cut without compression." 



Preservation of some Marine Animals.t— Mr. W. A. Reden- 

 baugh says that while spending a few weeks at the U.S. Fish 

 Commission Laboratory at Wood's Hole, Mass., he obtained some 

 interesting results with Epsom salts in the preservation of many 

 marine invertebrates. "The method of application requires 



*. Johns Hopkhis Hospital Bulletin, v., pp. 136 — 7. 

 \ American Xaturalist, XXix., 1895, pp. 399 — 401. 



