186 BAOTERIOLOOr. 



loidin acts as a cement; as it hardens rapidly, the 

 tissue is soon fast to the cork. The section is then 

 left in 60 per cent, alcohol for twenty-four hours to 

 complete the solidification of the celloidin, after which 

 sections may be cut in the way just described for tissues 

 not so treated. 



Imbedding in paraffin. After bits of the tissue not • 

 larger than a cubic centimetre have been hardened in 

 the usual way they are placed in fresh absolute alcohol 

 for twenty-four hours to complete the process. From 

 this they are transferred to pure turpentine, and kept in 

 a warm oven at a temperature not exceeding 36° to 

 38° C. Here they remain until thoroughly saturated 

 with the turpentine, as is recognized by the transparent 

 appearance they assume. From this they are placed in 

 paraffin that melts at 53° C, and allowed to remain in 

 this for three or four hours. They are then trans- 

 ferred to a small paper or metal mould, or a pill-box, 

 and melted paraffin is poured over thorn. When the 

 paraffin has become solid the mould or box is removed 

 from around it, the excess of paraffin trimmed from about 

 the imbedded tissue, and the latter is ready for cutting. 



When the sections are cut they are freed from par- 

 affin by exposing them to turpentine ; the latter is re- 

 moved by washing in alcohol and the sections can then 

 be stained in the ordinary way. In cutting sections 

 from tissues that have been imbedded in pai'affin the 

 long axis of the knife should be at nearly right angles 

 to the direction in which the knife travels. For bacte- 

 riological purposes the method of imbedding in jiaraffin 

 does not, as a rule, give such good results as ^\■llen the 

 celloidin method is employed. In this work, therefore, 

 the latter is usually preferred, 



