VI 

 METHODS OF CLEARING AND IMBEDDING 



The present section deals with the simplest methods of clear- 

 ing and Imbedding eggs. The reader may find these directions 

 too detailed and tiresome. It Is nevertheless necessary to 

 follow them because in the clearing and the Imbedding of minute 

 marine eggs, especially at the sea-side, a small mistake will 

 undo the long process that has gone before. The care exercised 

 in the preparation of sections is repaid by the ease and pleasure 

 which one enjoys in studying perfect preparations. 



Clearing 



The choice of clearing agents is wide. One may use among 

 others oil of bergannot, cedar-wood oil, chloroform, toluene or 

 xylene. Bergamot Is useful for it will clear after 90 per cent, 

 alcohol. Some of my best preparations are of eggs removed 

 from 95 per cent alcohol and cleared in cedar-wood oil. Both of 

 these oils may be refractory at the sea-side even when one has 

 the best grades. When used they should be followed by toluene 

 or xylene before Imbedding in paraffin. With chloroform one 

 must work quickly to avoid the taking up of moisture. On the 

 whole, the worker can depend upon toluene or xylene both for 

 clearing and for Infiltrating the eggs with paraffin. The objec- 

 tions often made against their use do not apply in the case of 

 minute objects such as marine eggs, provided the eggs do not 

 remain too long In them. One should however be at great- pains 

 to employ only the best grade of toluene or xylene which is 

 acid-free. Kept in large bottles, small volumes of either tend 

 to become acid in time. 



In the bath of the first toluene or xylene the absolute alcohol 

 is replaced by the oil. The small volume of alcohol remaining 

 should mix thoroughly with the oil without any trace of murki- 

 ness due to the presence of water. The second bath insures 



66 



