72 MATERIALS AND PROCESSES OF SLIDE-MAKING 



may be had to the method of frozen sections in which material is rapidly fro- 

 zen until it is of a consistency where it may be cut. Frozen sections should 

 not, however, be employed on any occasion when the normal processes of 

 embedding may be used. 



Choice of a Microtome. The type of microtome shown in Fig. 53 is 

 so universally employed that it will be taken as the basis for the present dis- 

 cussion. It is essential in cutting frozen sections that the knife slice, rather 

 than push, through the tissue. This slicing effect is produced by mounting the 

 knife to swing through the object when the handle on top is turned. These 

 microtomes are not as accurate, either as to the thickness of section cut or the 

 repetition of this thickness, as is the big Schantz shown in Fig. 32, but it is 

 to be presumed that no one would cut frozen sections, in any case, if thick- 

 ness and reproducibility were primary objectives. The method of freezing the 

 object will be discussed after we have dealt with the question of supporting 

 the material in a suitable medium. Even if one can spare only a few moments 

 in excess of the absolute minimum time required to cut without embedding, 

 better results will be obtained if one smothers the object in several layers of: 



Anderson's Medium: 

 Simple syrup 50 ml. 

 80% Alcohol 50 ml. 



White dextrin 15 Gm. 



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

 is added slowly and with constant stirring. Simple syrup, which may be obtained 

 from any pharmacist, is prepared by dissolving 5 lbs. of sugar in 2 pts. 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 micro- 

 tome, so that one has only to twist the valve to project a jet of super-cooled 

 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 has already been discussed. Assuming 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 sec- 

 tions 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. 



