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: Hemodynamic effects and histamine release by bolus injection of 0 . 35 mg / kg of d - tubocurarine were studied in 24 patients .
### Output Text:
Hemodynamic effects and <span class="chemical">histamine</span> release by bolus injection of 0 . 35 mg / kg of <span class="chemical">d - tubocurarine</span> were studied in 24 patients . 