In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Ventricular DNA content was unchanged during the early stage ( 1 - 4 days ) of hypertrophic growth but increased to a new steady - state level 19 % above the controls after 8 days of treatment .
### Output Text:
Ventricular DNA content was unchanged during the early stage ( 1 - 4 days ) of hypertrophic growth but increased to a new steady - state level 19 % above the controls after 8 days of treatment . 