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: In the present study , the possible enhancement by isoniazid of bradycardia induced by beta - adrenoceptor antagonists was determined in rats anaesthetised with chloralose - urethane .
### Output Text:
In the present study , the possible enhancement by <span class="chemical">isoniazid</span> of bradycardia induced by beta - adrenoceptor antagonists was determined in rats anaesthetised with <span class="chemical">chloralose</span> - <span class="chemical">urethane</span> . 