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: Preclinical murine studies demonstrated that the toxicity of lometrexol can be prevented by low dose folic acid administration , i . e . for 7 days prior to and 7 days following a single bolus dose .
### Output Text:
Preclinical murine studies demonstrated that the toxicity of <span class="chemical">lometrexol</span> can be prevented by low dose <span class="chemical">folic acid</span> administration , i . e . for 7 days prior to and 7 days following a single bolus dose . 