164 The Preparation of Microscope Slides 



Anderson's Medium: 



Simple syrup 50 ml 



80% alcohol 50 ml 



White dextrin 15 g 



Note: The dextrin is boiled to solution in the syrup and cooled; the 

 alcohol is added slowly and with constant stirring. Simple syrup, which 

 can be obtained from any pharmacist, is prepared by dissolving 5 lb of 

 sugar in 2 pt of water. 



Choice of Refrigerant. Blocks are nowadays almost invariably frozen 

 with the aid of carbon dioxide, which is available very cheaply in large 

 cylinders. The cylinder is connected through a needle valve to the object 

 holder of the microtome, so that one has only to twist the valve to project 

 a jet of supercooled carbon dioxide against the underside of the object 

 holder. 



Process of Cutting. The prime necessity for producing a good section 

 is, of course, the availability of a sharp microtome knife. The nature, care, 

 and sharpening of microtome knives have already been discussed. As- 

 suming that more than the minimum time is available and that the method 

 of Anderson is to be used, the following materials are required: a bottle 

 of Anderson's syrup, which is conveniently kept in a "balsam" bottle, a 

 pipette of the eye-dropper type, and a dish of 70 per cent alcohol in 

 which to receive the sections as they are cut. It is to be presumed also 

 that the carbon dioxide cylinder has been attached to the tube leading 

 to the microtome's freezing table and that a brief trial has been run to 

 make sure that the gas is flowing satisfactorily. 



About y 2 mi °f syrup is picked up with the pipette and placed on the 

 freezing table of the microtome. A small jet of carbon dioxide is then 

 turned on. Within a moment or two the gum will be seen to have con- 

 gealed, and the carbon dioxide is turned off. The object to be sectioned 

 is then ( Fig. 128 ) placed on top of this congealed layer of gum and more 

 gum is poured over the surface. Care must be taken that a layer of un- 

 congealed gum lies between the object and the congealed gum, or it 

 may loosen. The carbon dioxide is again turned on, and, as soon as the 

 gum covering the object is seen to be congealing, a little more syrup is 

 poured on the surface so that the object is thoroughly covered. It will be 

 seen from the figure referred to that, as a matter of convenience, the 

 knife has not yet been placed in its holder while these preliminary opera- 

 tions are going on. As soon as the knife has been inserted, an experimental 

 cut is taken across the top of the material with the knife, and the block 

 is then shaved down until the specimen is reached. The device that con- 

 trols the thickness of the section to be cut is then set to whatever thick- 

 ness has been decided upon. It is strongly recommended that no attempt 



