98 APPLIED BACTERIOLOGY 



melted para£6in--wax'; the prepared pieces of tissue are laid 

 on the centre of the wax layer, then more melted paraffin- 

 wax is poured on in such a way as to enclose the material in 

 the centre of a small block of wax. When set, which may 

 be hastened by immersion in cold water, the block is 

 trimmed to a suitable form with a knife to fit the clamp of 

 the microtome. The sections are cut without any moisten- 

 ing fluid. 



The sections are transferred to xylol in order to dis- 

 solve out the paraffin, after which they are placed 

 in absolute alcohol, and thence into water. If they do 

 not sink in water, the paraffin has not been properly re- 

 moved ; in this case they are put back to soak in alcohol 

 and xylol. 



Imbedding in Celloidine. — The alcohol- hardened portions 

 of tissue are fixed to bits of cork by means of a solution of 

 celloidine in a mixture of alcohol and ether ; and then, 

 after the celloidine has set, they are immersed in absolute 

 alcohol for some time (about twenty-four hours), when they 

 become of a suitable consistence for cutting. The pieces 

 are now soaked in a mixture of alcohol and ether, and 

 finally in a celloidine solution of medium consistency, in 

 which they remain for about twenty-four hours. The pre- 

 pared pieces are now allowed to dry in the air for a short 

 time, and then immersed in 30 per cent, alcohol for three 

 or four days. The celloidine becomes first cloudy and then 

 converted into an opaque, milk-white mass, which is of a 

 sufficient consistency to be cut by the microtome. By 

 this method the sections are saturated, so to speak, with 

 celloidine, which is capable of taking up the stain in the 

 same manner as the actual tissue. 



Very fine sections are obtained by this method even with 

 the most refractory materials ; for instance, satisfactory 

 preparations of actinomyces in sections can be obtained 



