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: Generally , atropine reduced contractions , but in contrast to controls , it also reduced responses to low electrical field stimulation intensity ( 1 - 5 Hz ) in inflamed preparations .
### Output Text:
Generally , <span class="chemical">atropine</span> reduced contractions , but in contrast to controls , it also reduced responses to low electrical field stimulation intensity ( 1 - 5 Hz ) in inflamed preparations . 