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: Accumulation of hepatic triglyceride , as a per cent of control values , in response to graded doses of tetracycline , did not differ significantly between male , female and pregnant rat livers .
### Output Text:
Accumulation of hepatic <span class="chemical">triglyceride</span> , as a per cent of control values , in response to graded doses of <span class="chemical">tetracycline</span> , did not differ significantly between male , female and pregnant rat livers . 