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: Caffeine increased plasma cortisol levels equally in the patient and healthy groups .
### Output Text:
<span class="chemical">Caffeine</span> increased plasma <span class="chemical">cortisol</span> levels equally in the patient and healthy groups . 