Preparation, etc., of Frozen Anatomical Sections. 355 



painting on glass with ordinary dry colours mixed with boiled 

 oil and a little turpentine. Ordinary tracing paper cannot be 

 placed directly upon the surface as it gets wet. If a thin sheet of 

 glass be placed between the section and the tracing paper the 

 outline of the different parts cannot be seen with sufficient 

 distinctness. Eibemont {^' BecliercJus sur V Anatomic Topo- 

 graphique du Fo&tiis" Paris, 1878) recommends that the 

 tracing paper be covered on one side with varnish and the 

 other placed against the glass. This makes the tracing 

 paper more transparent, but in my hands not sufficiently so. 

 The tracing paper is rendered still more transparent by 

 smearing it with boiled linseed oil, but tracing paper treated 

 in this way does not keep well. Painting on glass, although 

 a slower method than pencilling on tracing paper, is the best 

 plan I am aware of. 



The sections should be kept frozen until they have been 

 thoroughly examined, although the surface may be slightly 

 thawed to facilitate its examination. 



If it is desired to ascertain the position of any particular 

 part in the substance of the section, it can be thawed by 

 means of a hot iron, while the rest of the section is kept 

 frozen. 



The surface of a frozen section when well washed forms an 

 exceedingly beautiful preparation, and one not unnaturally 

 wishes that they could be preserved in that condition ; but if 

 allowed to thaw the softening of the tissues and their 

 unequal contraction causes the previously smooth surface to 

 become rough and irregular, and the relative position of the 

 parts is disturbed. 



If it is desired to keep the sections they should be made as 

 thin as possible, and carefully embedded close up to the cut 

 surface in Plaster of Paris while still frozen, and allowed to 

 thaw under methylated spirit. 



In a series of transverse sections of such parts as a limb, it 

 is generally recommended to make them about one and a half 

 or two inches in thickness, but sections half an inch will 

 keep much better. 



If the section passes through any cavities containing water. 



