the science of the causes and effects of diseases, especially the branch of medicine that deals with the laboratory examination of samples of body tissue for diagnostic or forensic purposes.
"Formaldehyde is used widely as a tissue preservative in pathology laboratories and embalming services."

Blood disooreders are classified into  those of blood and bone marrow diseases. Subclassification is give in more or less extended way there for 3rd and 4th year medical students.