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: Five patients developed universal hyperalgesia and hyperesthesia which in 2 cases were accompanied by myoclonus .
### Output Text:
Five patients developed universal hyperalgesia and hyperesthesia which in 2 cases were accompanied by myoclonus . 