68 BASIC METHODS FOR EXPERIMENTS 



one uses salt cellars selecting those with most wide-flaring sides 

 and flat bottoms. The salt cellars are easier to handle but the 

 watch crystals giving a more quickly solidifying block of greater 

 evenness are preferable. The watch crystal should be thor- 

 oughly dried by holding it over a flame before the eggs are 

 deposited in it. Avoid over-heating the crystal! 



The crystal containing the eggs is placed on an electric 

 hot-plate, the temperature of which is 6o°C. Before the eggs 

 become dried they should be flooded with paraffin melting at 

 6o°C. In this they are gently shaken up to insure diffusion of 

 what oil remains, then the dish is rotated to bring the eggs into 

 a solid drop. Paraffin is then removed and replaced by fresh. 

 The process of shaking the eggs, rotating the dish is repeated, 

 paraffin is removed again; the process repeated. This threefold 

 changing of the paraffin should not take more than 15 minutes, 

 ample time for the infiltration of the eggs by the parafl^in. 



It is of the utmost importance to use the best grade of paraffin 

 for imbedding eggs. Secure therefore from a reliable dealer a 

 transparent paraffin guaranteed to have been filtered. That 

 which comes in closely sealed tins is most practical; if it comes 

 wrapped in paper, remove it carefully to avoid its taking up 

 moisture, melt and filter it to insure its freedom from dirt. 

 Pour the melted paraffin in a tin with a tightly fitting cover. 



The melting point of the paraffin used is determined by the 

 temperature at which it is to be cut, the quality of the object to 

 be imbedded and the thinness of the sections to be made. In 

 general, one takes a paraffin of high melting point (a) for cutting 

 sections in the summer or in a warm room; (b) for brittle or hard 

 objects and (c) for cutting thin sections. Since the eggs after 

 fixation with the modified Meves are somewhat brittle and hard 

 and are best cut into sections from 3 to 6 microns either at the 

 temperature of the summer or in a warm room in winter, I 

 recommend the use of a paraffin melting at 6o°C. 



Also for less brittle and hard eggs, as those fixed with Bouin 

 or Carnoy or other fixatives, paraffin of 6o°C. melting point is 

 not too hard: for such the room temperature at the time of 

 cutting is easily adjusted. In addition, it is true that a paraffin 

 of 6o°C. melting point is much easier and quicker to manipulate 

 than one of a lower melting point. In my experience, paraffin 



