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: It was possible to suppress the increased ornithine decarboxylase activity with both beta - blockers in hypertrophied hearts , but there was no effect on the heart mass .
### Output Text:
It was possible to suppress the increased <span class="chemical">ornithine</span> decarboxylase activity with both beta - blockers in hypertrophied hearts , but there was no effect on the heart mass . 