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: Male rats were subcutaneously injected with morphine ( 10 mg / kg ) twice a day at 12 hour intervals for 10 days , and Rg1 ( 30 mg / kg ) was intraperitoneally injected 2 hours after the second injection of morphine once a day for 10 days .
### Output Text:
Male rats were subcutaneously injected with <span class="chemical">morphine</span> ( 10 mg / kg ) twice a day at 12 hour intervals for 10 days , and <span class="chemical">Rg1</span> ( 30 mg / kg ) was intraperitoneally injected 2 hours after the second injection of <span class="chemical">morphine</span> once a day for 10 days . 