HOSKINS: LABORATORY METHODS IN EMBRYOLOGY. 373 



For sectioning, the eggs should be removed from their mat- 

 rices and fixed in picro-sulfuric or some other good fixative. 

 Four per cent, formalin does not give good results except for 

 whole mounts, but probably ten per cent, would prove more 

 satisfactory. The extreme friability of the yolk material 

 makes the eggs difficult to section by ordinary methods. This 

 can be done easily, however, as follows : The eggs are cleared 

 in turpentine, then infiltrated with paraffin melting at about 

 54 degrees. They are then removed from the parafiin-bath, 

 and the paraffin alloived to harden. Afterwards they are 

 placed for a short time in 62-degree paraffin, so that the super- 

 ficial elements may become infiltrated with it, while the yolk 

 material is impregnated with the softer paraffin. This leaves 

 the eggs in sufficiently homogeneous condition to section well. 

 The blocks should first be cooled thoroughly, and then sectioned 

 quickly in a rather highly heated room so that only the outer 

 part of the paraffin becomes heated enough to permit the 

 sections to "ribbon." In this way the development of dis- 

 astrous stresses due to the disparity in consistency between 

 the various elements of the section is prevented. An electric- 

 light bulb suspended directly above the block and near enough 

 to warm one side of it facilitates matters by causing the paraf- 

 fin to ribbon better. 



For staining the sections, either Zwaardemaker's safranin 

 or h^em-alum and orange G. can be used, but almost any good 

 nuclear stain will do. 



Incidentally, it might be well at this point to refer to the 

 infiltrating apparatus used. It consists only of a fifty-candle- 

 power electric bulb suspended over the paraffin contained in 

 an ordinary glass tumbler or Stender dish. Its advantages 

 over the ordinary kinds of paraffin-baths are obvious. It is 

 entirely simple and the material is always infiltrated at the 

 lowest possible temperature — that of the barely melted par- 

 affin of the layer just above the solid part upon which it rests. 

 A bulb of lower candle-power can be used if a reflector is added 

 to concentrate the heat. Only the paraf!in in the upper part of 

 the container should be melted. This can be regulated by rais- 

 ing or lowering the electric bulb. 



Opportunity may be taken at this point to mention also a 

 section-knife that Doctor McClung, of this department, has 

 recently devised. Its purpose is to do away with the trouble 

 incident to keeping an ordinary knife in good condition. It 



2- Univ. Sci. Bull., Vol. IV, No. 18. 



