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: Among the common side effects of diphenylhydantoin ( DPH ) overdose , the most frequently encountered neurological signs are those of cerebellar dysfunction .
### Output Text:
Among the common side effects of <span class="chemical">diphenylhydantoin</span> ( <span class="chemical">DPH</span> ) overdose , the most frequently encountered neurological signs are those of cerebellar dysfunction . 