IMBEDDING METHODS. 83 



139. The Paraffin Bath.— The objects having been duly 

 saturated with a solvent, the next step is to substitute 

 melted paraffin for the saturating medium. 



Some authors lay great stress on the necessity of making 

 the passage from the saturating agent to the paraffin as 

 gradual as possible, by means of successive baths of mixtures 

 of solvent and paraffin kept melted at a low temperature, 

 say 35° 0. With oil of cedar, at all events, this is not 

 necessary. I simply put the objects into melted paraffin 

 kept just at its melting-point, and keep them there till they 

 are thoroughly saturated ; the paraffin being changed once 

 or twice for fresh only if the objects are sufficiently volu- 

 minous to have brought over with them a notable quantity 

 of clearing agent. If the objects have been for a very long 

 time — months or years — in the cedar oil, so that this has 

 become thick, I remove it partially or entirely by soaking 

 in xylol (30 minutes to several hours) before putting into 

 the paraffin. But with fresh oil of cedar I find no advantage 

 in doing so. 



Giesbeecht's method {Zool. Aiiz., 1881, p. 484), is as 

 follows : — Objects to be imbedded are saturated with 

 chloroform, and the chloroform and objects are gradually 

 warmed up to the melting-point of the paraffin employed, 

 and during the warming small pieces of paraffin are by 

 degrees added to the cl dor of arm. So soon as it is seen that 

 no more bubbles are given off from the objects, the addition 

 of paraffin may cease, for that is a sign that the paraffin 

 has entii'ely displaced the chloroform in the objects. This 

 displacement having been & gradual one, the risk of shrinkage 

 of the tissues is reduced to a minimum. 



Mayer {Grundzilge, Lee and Mayee, 1910, p. 84) first 

 saturates the objects with beiizol, and then adds to the 

 benzol some small pieces of paraffin, and lets them dissolve 

 in the cold. After several hours (up to eighteen) the whole 

 is brought in an open vessel on to the cold water-bath, the 

 bath is then warmed gradually so as to attain a temperature 

 of 60 C. in about two hours, and as fast as the benzol 

 evaporates melted para-ffln is added to it. Lastly, the 

 paraffin is changed once before the definitive imbedding. 

 He rarely leaves objects overnight in the water-bath. 



Apathy {Mikrotechnik, pp. 149, 150) first clears with oil 



