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: MJ disappeared when LTG dose was decreased by 25 to 50 % .
### Output Text:
MJ disappeared when <span class="chemical">LTG</span> dose was decreased by 25 to 50 % . 