390 ADDITIONS. 



remove then the slide to bottle of turpentine for a 

 few minutes until the paraffin is dissolved. Let the 

 turpentine drain from the slide. Place a streak of 

 rather thin balsam (dissolved in a mixture of chloro- 

 form and benzol) near one edge of the cover- slip, 

 and lower this gently on the sections. By this 

 method the tissue sticks to the shellac and the parts 



. of the section are not displaced on dissolving out 

 the paraffin. 



Instead of the shellac solution, equal parts of filtered white of 

 egg and glycerine to which a little thymol has been added, 

 may be used. The treatment is the same as that given above, 

 except that after the paraffin has been dissolved by turpentine, 

 the slide should be placed for a minute or so in absolute 

 alcohol. If required the sections can then be stained on the 

 slide. 



Celloidin. 



Imbedding in celloidin has the advantage that it is 

 not necessary to warm the tissue, and thus there is 

 little risk of the tissue shrinking. By the simple 

 celloidin method, however, such thin sections can- 

 not be obtained as by the paraffin method. But 

 when the tissue imbedded in celloidin is soaked in 

 gum, frozen and cut, this objection to the method 

 no longer holds. 



Celloidin solution. The celloidin solution is cut up 

 into small pieces and dissolved in a mixture of equal 

 parts of absolute alcohol and ether to make a fairly 

 fluid solution. It is sometimes advisable to use a 

 thicker solution after this. 



Treatment of tissue, (a) The tissue, dehydrated with 

 absolute alcohol after which it may be placed in a 

 mixture of absolute alcohol and ether or in ether 

 alone is placed in celloidin solution and left in it 



