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: With provision of adequate oleic acid as a substrate for the isolated perfused liver , a direct relationship was observed between dose of tetracycline and both accumulation of triglyceride in the liver and depression of output of triglyceride by livers from male and female rats .
### Output Text:
With provision of adequate <span class="chemical">oleic acid</span> as a substrate for the isolated perfused liver , a direct relationship was observed between dose of <span class="chemical">tetracycline</span> and both accumulation of <span class="chemical">triglyceride</span> in the liver and depression of output of <span class="chemical">triglyceride</span> by livers from male and female rats . 