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: Neither propranolol nor B 24 / 76 could stop the changes in the characteristic myosin isoenzyme pattern of the hypertrophied rat heart .
### Output Text:
Neither <span class="chemical">propranolol</span> nor B 24 / 76 could stop the changes in the characteristic myosin isoenzyme pattern of the hypertrophied rat heart . 