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: Shortly after treatment their tests normalized and during follow - up period none of the patients had abnormal liver function tests .
### Output Text:
Shortly after treatment their tests normalized and during follow - up period none of the patients had abnormal liver function tests . 