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: Immunohistochemical , electron microscopic and morphometric studies of estrogen - induced rat prolactinomas after bromocriptine treatment .
### Output Text:
Immunohistochemical , electron microscopic and morphometric studies of <span class="chemical">estrogen</span> - induced rat prolactinomas after <span class="chemical">bromocriptine</span> treatment . 