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: Because knowledge of stone composition is essential for studies of their pathogenesis , treatment , and prevention , this was investigated by direct and indirect methods in 14 octreotide treated acromegalic patients with gall stones .
### Output Text:
Because knowledge of stone composition is essential for studies of their pathogenesis , treatment , and prevention , this was investigated by direct and indirect methods in 14 <span class="chemical">octreotide</span> treated acromegalic patients with gall stones . 