Please be careful when you are going to get the samples from the body of the animal, it is extremly important to use the most soft fixing solution. I prefer to use Bouin Solution:

      Picric acid (saturated) ------------------- 75 ml

      Formaldehyde (37-40%) ------------------ 25 ml

      Glacial acetic acid ------------------------- 5 ml  

      Mix well.

For routine surgical material, especially for preserving soft and delicate structures such as brain tissues, gut of lymphatic nodes .After 24 hours wash in 70% ethanol and keep in 70% ethanol if you need. It is necessary to use the ratio of 1 to 10 -20 (volume of tissue and solution)