CH. A] PARAFFIN METHOD 291 



infiltrated a day or two in-thick mucilage before freezing. Drop a 

 little thick mucilage on the top of the freezer, put the tissue in the 

 mucilage and turn on a small amount of carbon dioxid. It will 

 soon freeze the mucilage and the tissue as shown by the white 

 appearance. When frozen, cut the tissue rapidly. It is well to 

 have an assistant turn the feed screw up while the sections are cut. 

 When 20 or 30 sections are cut place them in water or normal salt 

 solution. The staining and mounting of the sections will be con- 

 sidered in § 461-471. This is a rapid method of getting sections 

 much used in pathology where quick diagnoses are demanded. In 

 normal histology the freezing microtome is used mostly for organs 

 or parts of greatly varying density. For example if one wishes sec- 

 tions of the finger and finger nail, this apparatus offers about the 

 only means of getting good sections. In that case the bone is decal- 

 cified before trying to make the sections (§ 398). 



THE PARAFFIN METHOD OF SECTIONING 



§ 439. Object of the Paraffin. — In the early periods in his- 

 tology great difficulty was encountered in making good sections of 

 organs and parts of organs because the different tissues were very, 

 unlike in density. At first tallow and beeswax, elder pith, liver 

 and various other substances were used to enclose or surround the 

 object to be cut. This gave support on all sides, but did not render 

 the object homogeneous. In the early sectioning, a great effort 

 was made to keep all imbedding material from becoming entangled 

 in the meshes of the tissue. This was guarded against by coating 

 the object with mucilage, and hardening it in alcohol. This muci- 

 lage jacket kept the tissue free from infiltration by the imbedding 

 mass and itself was easily gotten rid of by soaking the sections in 

 water. 



A great advance was made when it was found that the imbed- 

 ding mass could be made to fill all the spaces between the tissue 

 elements and surround every part, the tissue assuming a nearly 

 homogeneous consistency, and cutting almost like the clear imbed- 

 ding mass. Coco butter was one of the first substances to be used 

 for thus "infiltrating" the tissues. The imbedding mass must be 

 removed before the staining and mounting processes. 



§ 440. Infiltration of the Tissue with Imbedding Mass. — 



