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: Three of these cases were from the 25 transplantations performed at King Fahad National Guard Hospital , while the other 2 transplantations had been performed abroad and were referred to us for follow - up .
### Output Text:
Three of these cases were from the 25 transplantations performed at King Fahad National Guard Hospital , while the other 2 transplantations had been performed abroad and were referred to us for follow - up . 