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: During the follow - up period , attention was paid to breast modifications as evidenced by symptomatology , physical examination , and plate thermography .
### Output Text:
During the follow - up period , attention was paid to breast modifications as evidenced by symptomatology , physical examination , and plate thermography . 