496 HISTOLOGY 



Paraffin Celloidin 



95 per cent, alcohol 12-24 hr. 95 per cent, alcohol 12-24 hr. 



Absolute 1 2-24 hr. Absolute 12-24 hr. 



Absolute and chloroform, equal parts. 2- 6 hr. Absolute and ether, equal 



Chloroform 2- 6 hr. parts 12-24 hr. 



Chloroform saturated with paraffin. 2- 4 hr. Thin celloidin 24 hr. to a week 



Melted paraffin 2- 4 hr. Thick celloidin 24 hr. to a week 



Imbed in fresh melted paraffin and cool quickly. Mount on fiber block; harden and preserve in 



80 per cent, alcohol. 



3. Cutting and Handling Sections. 



Paraffin Sections. Two kinds of microtomes are in general use for 

 sectioning objects imbedded in paraffin. In one form, the "precision 

 microtome," the knife is horizontally placed and the object is moved 

 backward and forward on a carrier. In the rotary microtome, the knife 

 is vertically placed and the object is moved up and down, being cut on 

 the down stroke. In both forms, the knife edge is at right angles to the 

 carrier and the object. 



For sectioning with the precision microtome, the object is mounted on 

 a fiber block which is then clamped in the microtome; with the rotary 

 form, it is mounted on a special metal, disc. Before attaching the im- 

 bedded object, superfluous paraffin is cut away, leaving the tissue rising 

 from a broad base and completely surrounded by a thin layer of paraffin. 

 The block should be trimmed so as to give a rectangular or square surface 

 to be cut, and there should be a considerable layer of paraffin between the 

 object and the block or disc to which it is to be attached. The base is 

 placed upon a heated spatula which rests upon the fiber block. When 

 the paraffin is somewhat melted, the spatula is withdrawn and the base 

 is pressed down upon the block, to which it adheres when the paraffin 

 solidifies. In mounting upon the metal disc, the disc is heated, the block 

 pressed upon it and the whole quickly cooled by immersing in water. 



If the paraffin on each side of the object is trimmed parallel with the 

 knife edge, the successive sections adhere to one another, forming ribbons. 

 As they are taken from the knife, the ribbons are laid in a shallow box. 

 By placing them in order, they may later be attached to the slide in per- 

 fect series, one after the other. The first one cut is attached to the upper 

 left hand corner, and the others follow like lines on a printed page. Sec- 

 tions mounted in this way are called serial sections. The sections should 

 be from 5 to 10 fj. in thickness, but under favorable conditions thinner 

 sections may be secured. 



Before they can be stained, paraffin sections must be attached to the 

 slide and the paraffin must be removed. To attach them to a slide, a 

 mixture of equal parts of white of egg and glycerin is used. The white 

 of egg is thoroughly stirred and filtered. An equal volume of glycerin is 

 added, the two thoroughly mixed and a small lump of camphor added as 



