Blade fixations

Figure 4-102. Blade fixations redesigned to effect rapid repair.

We found that solutions of hen egg white lysozyme, bovine ribonuclease A (RNase A), or a 1 2 mol ratio of bovine carbonic anhydrase lysozyme formed opaque gels within 2 min when mixed with an equal volume of 20% NBF.25,26 Multi-protein tissue surrogates comprised of 50% w/v lysozyme and up to four additional proteins have also been formed (Fowler et al., unpublished results). After overnight fixation, the surrogates were firm and sliced easily with a razor blade for sampling. To determine the optimal... 

Visceral Fetal Examinations. The examination of the abdominal and thoracic viscera of fetuses is performed either fresh without fixation ( Staples technique ) or after Bouin s fixation by making freehand razor blade sections ( Wilson s technique Wilson, 1965). Both techniques have advantages. The fresh examination technique, which may require less training for thorough proficiency, provides a more easily interpreted view of heart anomalies. The examination must be performed on the day the dam is terminated, however, so having a large number of litters to examine in one day requires that a large team of workers be committed to the task. 

Evaluation of the internal structures of the fetal rat and rabbit head has traditionally been performed after fixation, most commonly in Bouin s fluid, by assessing serial coronal sections, prepared using a freehand blade to cut the specimen (1, 2). Whilst this method is widely accepted, both by users and regulatory authorities, it does have major drawbacks that are often overlooked because of its widespread use. These include ... 

If no other histochemical techniques are needed, fresh tissue can be used. The block must be frozen quickly without cracking. Tissue is cut in small blocks with a new razor blade (washed in soap to remove oil). An alternative to the method below is freezing tissue on aluminum foil on top of dry ice and surrounding with crushed dry ice. However, the perimeter of the tissue is usually poorly preserved with this method. For RNA detection, DEPC is included at 0.02% in the subbing and fixation solutions. Poly-L-lysine coating may be superior at temperatures > 50°C since gel from gel-coated slides may detach at higher hybridization temperatures. It is convenient to use only some of the slides for immediate hybridization and store the rest for future reference. 

After a total of 4-5 min of fixation, freeze the slide by immersion in liquid Na (it is helpful to hold the slide gently using a pair of hemostats, the tips of which are covered with silicone rubber tubing). After 15-20 sec, remove the slide and as quickly as possible, crack off the cover slip with a fresh razor blade. Immediately transfer the slide to a Coplin jar/staining dish filled with either 95% EtOH or 100% MeOH, prechilled to -20°C. Cover slips can be reused, if you find them. 

Heller and Bernal and Fankdchen have pointed out the possibility of explaining gel-formation in sols with rod-shaped or blade-shaped particles by assuming a local orientation and fixation of particles by long range forces, the whole system being solidified by a network of chains of particles thus held more or less rigidly near to each other. Fig. (27). 

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