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: Although reasonable incidences of many of these side effects can be " softly " deduced from current reports dealing with unfractionated heparin , at present the incidences of these side effects with newer low molecular weight heparins appear to be much less common .
### Output Text:
Although reasonable incidences of many of these side effects can be " softly " deduced from current reports dealing with unfractionated <span class="chemical">heparin</span> , at present the incidences of these side effects with newer low molecular weight <span class="chemical">heparins</span> appear to be much less common . 