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 degree of these seizures increased with increasing concentration of tAMCA .
### Output Text:
The degree of these seizures increased with increasing concentration of <span class="chemical">tAMCA</span> . 