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: In addition , OCT improved mineralization lag time , ( that is , the rate at which osteoid mineralizes ) in both Nx and Sham dogs .
### Output Text:
In addition , <span class="chemical">OCT</span> improved mineralization lag time , ( that is , the rate at which osteoid mineralizes ) in both Nx and Sham dogs . 