84 CHAPTER VIII. 



of cedar, then brings the objects (by the process described 

 § 119) into a solution of paraffin in chloroform saturated at 

 the temperature of the laboratory. The objects remain in 

 the chloroform-paraffin solution for from one to three hours, 

 without warming, until all the cedar oil is soaked out of 

 them. The whole is then warmed on the water-bath or 

 oven to a few degrees above the melting-point of the paraffin 

 intended to be used for imbedding, and the object is brought 

 into a mixture of equal parts of paraffin and chloroform, 

 being suspended therein near the top on a bridge made of 

 hardened filter paper (or in a special apparatus to the same 

 end, not yet described). It remains in this mixture, at the 

 temperature of the oven, for one to three hours, and lastly 

 is brought (still on the paper bridge or in the apparatus) 

 into pure paraffin, where it remains for half an hour to two 

 hours. 



Denne (m litt., 1907) points out that the objects ought at 

 first to be at the bottom of the mixture. For this mixture 

 is not a true solution, and the lower section of the contents 

 of the tube is comparatively free from paraffin while the 

 upper part is nearly pure paraffin. He moves the holder 

 up in the tube at intervals, and the infiltration proceeds 

 gradually with the minimum risk of shrinkage. Lastly, he 

 removes the objects, on the holder, to the top of a tube 

 of pure paraffin. 



The practice of giving successive baths first of soft and 

 then of hard paraffin, which has been frequently advised, 

 appears to me entirely illusory. 



It is important to keep the paraffin dry — that is, protected 

 from vapour of water during the bath. 



It is still more important to keep it as nearly as possible 

 at melting-point. If it be heated for some time to a point 

 much over its normal melting-point, the melting-point will 

 rise, and you will end by having a harder paraffin than you 

 set out with. And as regards the preservation of tissues, of 

 course, the less they are heated the better. Overheating, as 

 well as pi'olonged heating, tends, amongst other things, to 

 mahe tissues brittle. 



The duration of the bath must, of course, vary according 

 to the size and nature of the object. An embryo of 2 to 3 

 millimetres in thickness ought to be thoroughly saturated 



