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: In this patient the time relation between the ingestion of diphenylhydantoin and the occurrence of the skin rash , lymphadenopathy and pure red cell aplasia is very suggestive of a direct connection .
### Output Text:
In this patient the time relation between the ingestion of <span class="chemical">diphenylhydantoin</span> and the occurrence of the skin rash , lymphadenopathy and pure red cell aplasia is very suggestive of a direct connection . 