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: Focal injury in the cortex was produced by infusion of lactate at acid pH or by stab caused by needle insertion .
### Output Text:
Focal injury in the cortex was produced by infusion of <span class="chemical">lactate</span> at acid pH or by stab caused by needle insertion . 