26 STUDENTS HISTOLOGY 



Sections of exquisite thinness may now be cut. The knife need 

 not be wet. Paraffin imbedding is especially adapted to making 

 serial sections. 



In order to mount the sections, proceed as follows: 



a. Place the sections on a slide. Add a thin solution of gum 

 arabic, upon which they float. Warm slightly, when the sections 

 will flatten nicely. Drain off the superfluous gum solution, leaving 

 the sections in their proper positions. Let them dry for some 

 hours, and they will be firmly fastened to the slide. 



b. Dissolve out the paraffin in one of the numerous solvents 

 (xylol, half an hour or less). 



c. At this point, unless the piece of tissue was stained in bulk 

 before imbedding, the xylol should be washed off with alcohol and 



d. The section stained with one of the dyes described here- 

 after. 



e. Dehydrate in alcohol. 



/. Clear in some suitable agent, as xylol or oil of cloves. 

 g. Mount in balsam. 



CELLOIDIN INFILTRATION 



Certain structures require permanent support i.e., not only 

 while being cut, but during the subsequent handling of the sec- 

 tions. The celloidin infiltrating process is best adapted to such 

 material. Considerable time is needed for the successful employ- 

 ment of the process, but results can be secured that cannot be 

 equaled with any other method. 



Celloidin is the proprietary name of a sort of pyroxylin, very 

 soluble in a mixture of ether and alcohol, producing a collodion. 

 If thick collodion be exposed for a few moments to the air it 

 becomes semi -solid not unlike boiled egg -albumen; and to this 

 property is due the value of a solution of celloidin in histology. It 

 may be used as follows: 



To a mixture of equal parts of ether and alcohol add celloidin* 

 until the thickest possible solution has been obtained. 



A piece of alcohol -hardened tissue, having been selected and 

 kept for the preceding twenty -four hours in a mixture of equal 

 parts of alcohol and ether, is placed in about an ounce of the solu- 



*We find, after repeated trial, that the ordinary soluble gun-cotton, such as is employed by 

 photographers, is in no way inferior to the celloidin. 



