76 Nitrocellulose Method (chap. 7) 



Walls (1932) used bottles with thick lips and corks, and wired on the 

 corks with a wire wound under the lip and over the cork. High pressure 

 builds up in the bottle, and together with the high viscosity of the 

 heated celloidin produces rapid penetration. He maintains that heat is 

 of no concern in this method; in the paraffin method it is the hot paraffin, 

 not the heat itself which, if used too long, produces a brittle block. 



Do not hurry the cooling process; leave warm bottles on a wooden 

 table top until they have reached room temperature and they will not 

 break. 



Difficulties in Nitrocellulose Sectioning^ 



1. Scratches in sections. Caused by: 



a. nick in knife. 



b. hard material in tissue. 



c. position where knife ^vas stopped while unrolling section. 



2. Tissue soft, mushy, crumbles or falls out. Caused by: 



a. imperfect infiltration due either to incomplete dehydration or 

 too short a time in nitrocellulose. Reinfiltrate. 



b. embedding too rapid, as in short method. 



3. Sections vary in thickness. Caused by: 



a. worn parts in microtome. 



b. pressing too hard on knife block. 



c. insufficient hardening of nitrocellulose. Too soft and compresses 

 under knife. 



d. tissue block is rising before return stroke of knife has cleared it. 



e. insufficient tilting of knife. Shoulder of facets compresses block 

 instead of cutting it and next section is thick. 



/. embedding too rapid, as in short method. 



Staining and Mounting 



Sections are stained before motmting in this method. Staining may be 

 handled in Syracuse watch glasses or similar flat dish. With forceps or 

 spatula carry the sections through successive watch glasses and follow 

 each change by draining the section against a paper towel or filter pa- 

 per. In this way, contamination can be held to a minimum. If, however, 

 the solutions do pick up considerable stain, change them as frequently 

 as seems necessary, or even more often. Also, if they have remained un- 



1 Modified after Richards, 1949. 



