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: These findings demonstrate that some neuroactive steroids attenuate convulsant and sensitizing properties of cocaine and add to a growing literature on their potential use in the modulation of effects of drugs of abuse .
### Output Text:
These findings demonstrate that some neuroactive <span class="chemical">steroids</span> attenuate convulsant and sensitizing properties of <span class="chemical">cocaine</span> and add to a growing literature on their potential use in the modulation of effects of drugs of abuse . 