176 IMBEDDING METHODS. 



1892, p. 200) to be a cause of shrinkage in cells; he employs 

 oil of bergaraot. 



Chloroform mixes well with paraffin, and after evaporation 

 in a paraffin bath (in the manner described in the next para- 

 graph) leaves behind a pure and very homogeneous paraffin, 

 having but little tendency to crystallise. But it is deficient 

 in penetrating power, so that it requires an excessive length 

 of time for clearing objects of any size ; and it must be very 

 thoroughly got rid of by evaporation in the paraffin bath, or 

 by successive baths of paraffin, as if the least trace of it 

 remains in the paraffin used for cutting it will make it soft. 

 Chloroform ought, therefore, to be reserved for small and easily 

 penetrable objects. 



Cedar-wood oil is, according to my continued experience, 

 for the reasons stated by me in Zool. Anz., 1885, p. 563, in 

 general the best clearing agent for paraffin imbedding. It 

 penetrates rapidly, preserves delicate structure better than 

 any clearing agent known to me, does not make tissues brittle, 

 even though they may be kept for weeks or months in it, and 

 has the great advantage that if it be not entirely removed from 

 the tissues in the paraffin bath it will not seriously impair the 

 cutting consistency of the mass ; indeed, I fancy it sometimes 

 improves it by rendering it less brittle. 



In some difficult cases anilin oil is indicated (see 353). 



276. The Paraffin Bath. The objects having been duly 

 " penetrated " or " cleared," the next step is to substitute 

 melted paraffin for the penetrating or clearing medium. 



Some authors lay great stress on the necessity of making 

 the passage from the clearing agent to the paraffin as gradual 

 as possible, by means of successive baths of mixtures of clearing 

 agent and paraffin kept melted at a low temperature, say 35 C. 

 With oil of cedar or toluol, at all events, this is not necessary. 

 All that is necessary is to bring the objects into melted paraf- 

 fin 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 voluminous 

 to have brought over with them a notable quantity of clearing 

 agent. 



The practice of giving successive baths first of soft and then 

 of hard paraffin appears to me entirely illusory. 



