IQ2 BACTERIOLOGICAL DIAGNOSIS. 



Where time permits it is a great advantage to rinse 

 the section in distilled or clear rain water after re- 

 moving it from the haematoxylin. 



The solution of haematoxylin is best bought ready 

 made, as its preparation is somewhat difficult. Dela- 

 neld's solution is about the best for general work. 



A counterstain is not really necessary for diagnostic 

 purposes, and its omission hastens the process some- 

 what. 



THE PARAFFIN PROCESS. 



Tissues which are to be cut in paraffin may be hard- 

 ened in any of the fluids mentioned above. They are 

 then dehydrated, cleared in chloroform or other fluid 

 which mixes with alcohol and dissolves paraffin, and 

 finally soaked in a mixture of hard and soft paraffin 

 kept just at the melting point. This paraffin should 

 be obtained specially for the purpose ; the Cambridge 

 paraffin is the best. It is made in two varieties, the 

 soft, which melts at 48 C., and the hard, which melts 

 at 55 C. The amounts of each which should be used 

 for embedding depends upon the external temperature ; 

 in very hot weather hard paraffin may be used alone, 

 while under average circumstances a mixture of equal 

 parts of each is best. 



We shall now proceed to describe the various pro- 

 cesses seriatim. 



DEHYDRATION. 



This is very simple. The blocks of tissue are placed 

 in weak spirit for a few hours or for a day, then 



