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: A rare case of morbid vasospasm , together with striking angiographic findings , is described secondary to the ingestion of methysergide by a 48 - year - old woman .
### Output Text:
A rare case of morbid vasospasm , together with striking angiographic findings , is described secondary to the ingestion of <span class="chemical">methysergide</span> by a 48 - year - old woman . 