Rodent tissues are inherently lower in fat and with less water in their fat tissue and this is a "dangerous" combination when processing because, as you point out, the tissues you received are overprocessed so you will have ptoblems sectioning, extending the sections and holding them to your slides.
Try ALL the following steps:
1- prepare a solution of 0.2% (v/v) of fabric softener and prepare a frozen block with it. This frozen 0.2% fabric softerner will be used to cold the blocks. Face them off and place them face down over the frozen softener covered with paper towels in a way that the blocks are going to be in contact with the softener for at least 30 minutes before trying to section.
2- increase the temperature of your water bath at 50-52║C, close to the paraffin melting point WITHOUT reaching it.
3- add to your water bath 0.25 mL of liquid detergent (but NOT dish washer). This step, and the previous one are designed to lower the water surface tension and facilitate the sections expansion.
4- add 1 mL of Elmer's (white) glue to the water bath. The water will be slightly whitish but this weak glue solution will help to hold the sections to the slides.
When you get to the area in the block that you want to section, cool it with a ice cube wrapped in a gauze and take the sections SLOWLY.
This combinaiton should help you, but all the steps together.
Good luck with your rodents' blocks!
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