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: Over the period 1993 - 1996 , 551 cases of VTE were identified in Germany and the UK along with 2066 controls .
### Output Text:
Over the period 1993 - 1996 , 551 cases of VTE were identified in Germany and the UK along with 2066 controls . 