If your liver sections are consistently, and annoyingly cracked, you may
want to re-examine you processing schedule.  Rat tissues can be overexposed
(sometimes called overprocessing) to dehydrants, clearants, and heat of
paraffins.  A shorter processing schedule may be needed and adding lower
concentrations of alcohols at beginning.  1 hour per station for rat
spleens and livers has proven drying in our lab, and even with shorter
processing we will need some soaking with ice water. We never add heat to
processing in dehydrants or clearants, just ambient temps.   

Example, 50%, 70, 80, 95 X 2, 100 X 2, xylene X 2 (better yet single
aliphatic hydrocarbon xylene substitute X 2 as xylene contributes to
hardness at times) then no more than 2 hours total in ALL paraffins.  This
will depend on you processor, some have 3 stations, some only have 2 or
even 4.  Divide up the total time between each station.  You may find the
two hours is a bit long, so subtract time. Example, paraffins X 3 with
times 30, 30, and 45 min for three stations. 

Good luck 
Gayle Callis
MT,HT,HTL(ASCP)
Research Histopathology Supervisor
Veterinary Molecular Biology - Marsh Lab
Montana State University - Bozeman
19th and Lincoln St
Bozeman MT 59717-3610

406 994-6367 (voice mail)
406 994-4303 (FAX)

email: UVSGC@montana.edu