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: Thromboemboli were venous ( 12 patients , 7 with pulmonary emboli ) or arterial ( 4 patients ) or both .
### Output Text:
Thromboemboli were venous ( 12 patients , 7 with pulmonary emboli ) or arterial ( 4 patients ) or both . 