Word categories present in the five sections under analysis. Classes according to MeSH are A (Anatomy), B (Organisms), C (Diseases), D (Chemicals & Drugs), E (Techniques & Equipment), G (Biological Sciences). An additional class X was defined in this work (Units, Dimensions, & Parts). The number of words used for the analysis was 36 (class A), 14 (B), 11 (C), 47 (D), 33 (E), 41 (G), 49 (X). (a) Average number of occurrence of words of each subset per section. (b) Frequency of words of each subset per total number of words for each section.