Library books are arranged by the Dewey Decimal classification scheme whereby each subject is represented by a number.
You wil find books on the same subject will have the same number. The shelfmark is preceded by the letter D and will be followed by 3 letters, which are usually the first 3 letters of the author's name.
Here are some useful biological and biomedical science shelfmarks.
D 574.1 Physiology
D 574.19 Biochemistry
D 574.2 Pathology
D 574.8 Tissue & molecular biology
D 576 Microbiology
D 612 Human physiology
D 612.01 Human biochemistry
D 615 Pharmacology and therapeutics
D 615.7 Pharmacodynamics
D 664 Food technology