32 



or 05% alcohol and the section (or sections) will float free and sink 

 to the bottom. 



71. Serial Sectioning. If it is desired to mount the sections 

 in series, proceed as follows: With a. camel's hair brush or needle 

 draw the first section, when cut, up toward the back of the knife and 

 make the next section. Place this section to the right of the first, and 

 so on, arranging them in serial order, section after section, and line 

 below line, until enough are cut to fill the area that the cover-glass will 

 cover. Flood the sections as before by letting the clarifier flow over 

 them, being careful, however, not to float them from their places. 

 Absorb the clarifier from the knife with a pipette, and place over 

 the sections a piece of the transfer paper twice the width of a slide; 

 press it down if necessary, and slowly draw it off the edge of the 

 knife. Should it then be seen that some of the sections are adhering 

 to the knife instead of the paper, it means that the clarifier had been 

 allowed to thicken* on them, cementing them to the knife, and the 

 preliminary flooding to insure their being free, was insufficient. In 

 that case it is best to flood the paper with clarifier, carefully lift it, 

 arrange the sections again, flood them with clarifier, place a clean 

 piece of transfer paper over them and try again. One soon becomes 

 accustomed to the behavior of the sections, and accidents are rare. 

 In cutting a series of many small sections, some time is consumed 

 and it is necessary to flood the sections on the knife frequently with 

 clarifier while cutting in order to prevent the clarifier thickening and 

 cementing them to the knife. 



72. Resume of the method. Success in the employment of 

 the celloidin or collodion method depends upon the thorough infil- 

 tration with the solutions, requiring days or even months, and the 

 employment of a thick imbedding mass giving when hardened a firm 

 unyielding support to the tissue. This may be gained by employing 

 a relatively long period of infiltration, and taking pains in imbed- 

 ding to have the imbedding mass well thickened. 



Observing these two cautions, celloidin may be used in almost 

 all cases as an imbedding mass, except such as are affected by the 

 conditions of the methods already mentioned ( 47 and 61). 



*If one is a long time cutting a series of sections, it sometimes occurs that 

 the xylene evaporates leaving the castor oil that is thick and viscid and also 

 a solvent of the collodion, so that the sections are not easily transferable but stick 

 rather firmly to the knife. In such a case, fresh clarifier or even a little xylene 

 to dissolve the castor oil must be used. 



