Il8 DEMONSTRATING BACTERIA IN TISSUES 



chloroform. On the surf ace, of the chloroform float 

 a layer of absolute alcohol about five to ten millimetres 

 in depth. Place the pieces of tissue in the layer of 

 alcohol and when they have sunk through this layer, 

 transfer them to pure chloroform for from six to 

 twenty-four hours according to the size of the pieces. 

 When "cleared," the tissue becomes more or less 

 transparent. 



6. Infiltration. Place the cleared tissues in fresh 

 chloroform with several pieces of paraffin wax and 

 stand in a warm place, such as on the top of the warm 

 incubator. The warmth gradually melts the paraffin 

 and the tissues should remain in the mixture about 

 twenty-four hours. 



7. Transfer the tissues to a vessel containing pure 

 melted paraffin. Place this vessel in a paraffin water- 

 bath regulated for 2 C. above the melting-point of the 

 paraffin used, and allow the tissues to soak for some 

 four to six hours to ensure complete impregnation. 

 The paraffin used should have a melting-point of not 

 more than 58 C. For all ordinary purposes 54 C. 

 will be found quite high enough. 



8. Imbed in fresh paraffin in a metal (or paper) 

 mould. 



(a) Arrange a pair of L-shaped pieces of metal on 

 a plate of glass to form a rectangular trough (Fig. 72). 



(6) Pour fresh melted paraffin into the mould from a 

 special vessel (Fig. 73). 



(c) Lift the piece of tissue from the paraffin bath 

 and arrange it in the mould. 



(d) Blow gently on the surface of the paraffin in the 

 mould, and as soon as a film of solid paraffin has formed, 

 carefully lift the glass plate on which the mould is set 

 and lower plate and mould together into a basin of 

 cold water. 



(e) When the block is cold, break off the metal L's; 

 trim off the excess of paraffin from around the tissue 



