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: The proportion of patients with major and intracranial bleeding increased from 20 . 2 % and 1 . 9 % , respectively , in the first time period , to 33 . 3 % and 7 . 8 % , respectively , in the second .
### Output Text:
The proportion of patients with major and intracranial bleeding increased from 20 . 2 % and 1 . 9 % , respectively , in the first time period , to 33 . 3 % and 7 . 8 % , respectively , in the second . 