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: Abnormal movements and deafness occurred only in rats treated during the preweaning period ; within this period the greatest sensitivities for these abnormalities occurred from 2 to 11 - 17 and 5 to 11 days of age , respectively , indicating that the cochlea is more sensitive to streptomycin than the site ( vestibular or central ) responsible for the dyskinesias .
### Output Text:
Abnormal movements and deafness occurred only in rats treated during the preweaning period ; within this period the greatest sensitivities for these abnormalities occurred from 2 to 11 - 17 and 5 to 11 days of age , respectively , indicating that the cochlea is more sensitive to <span class="chemical">streptomycin</span> than the site ( vestibular or central ) responsible for the dyskinesias . 