FROZEN SECTIONS. 131 



This rule may sometimes require modification, as with some " fislies" witli delicate caudal 

 fins, which might be broken by the pressure. The specimen may be suspended from the 

 cover of the jar, or the tail may rest upon cotton, or, finally, the jar may be of such size as 

 to permit the withdrawal of the specimen tail first. 



§ 831. In some cases, when a delicate or valuable specimen is in a jar or vial with a 

 mouth too small for its easy or safe extraction, the jar should be sacrificed. Place its 

 mouth just over the edge of a waste pail or box, and rap it. smartly with a hammer so as 

 to break off the top. In removing the specimen, avoid the bits of glass which may have 

 fallen into the jar. 



When the glass stopper of a jar cannot be removed in the ordinary way, tap the han- 

 dle on both sides, alternately, with a piece of wood or the edge of a razor-strop. If this 

 fails to loosen the stopper, or if the handle breaks off, the jar may be broken open as 

 directed above. 



§ 322. In removing large specimens from alcohol, especially if the hair or feathers 

 remain, squeeze the alcohol out with the hands, then suspend the specimen for a short 

 time from a hook over the jar or some other receptacle, and finally rinse it oS with a 

 stream of water. In this way some alcohol is saved, drying is retarded, and the dissector 

 avoids the odor and stimulating effect of the vapor of the alcohol. 



FROZEN" SECTIONS AND DISSECTIONS. 



§ 323. Frozen Sections. — These are sections of desired thick- 

 ness made of a specimen which has been frozen Jiard so that the 

 parts retain their natural relative positions. 



Such preparations have been made in Europe since 1833, and in some cases they have 

 been preserved as permanent preparations. A series of frozen sections of the head, in the 

 museum of the Medical School of Maine, were made by Dr. Thomas Dwight, and formed 

 the basis of his work on the head (A). See also his more recent work (B). 



Frozen sections of a cat were made by us on the 21st of Jan., 1879, and were briefly 

 described by the senior author in 21. The method was as follows : — 



§ 324. The cat was killed with chloroform, the arteries injected 

 with red plaster and the veins with blue. It was then carefully 

 supported in a natural attitude in a box of hay, which was placed 

 out of doors for three days. The cat was then perfectly rigid, and 

 was rapidly cut with a sharp wide-bladed saw into transections 

 about 1 cm. thick. The cutting was done in a cool room, and each 

 section when made was placed upon a glass plate, held under a 

 gentle stream of water, and both surfaces freed from hair and fat 

 particles with a soft nail brush. It was then laid on one side in a 

 dish of 95 per cent, alcohol, and put in a cool place. 



As the sections thawed, they were hardened by the alcohol so 

 as to retain their form. Each was then mounted in a compressed 

 jar (§ 316). In some cases the viscera were secured from falling 

 out by means of insect pins. The cavities of the heart were better 

 seen after the removal of the plaster. 



