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: Gastrointestinal toxicosis was detected in 37 . 8 % of dogs , the most common sign of which was vomiting ( 24 . 3 % ) .
### Output Text:
Gastrointestinal toxicosis was detected in 37 . 8 % of dogs , the most common sign of which was vomiting ( 24 . 3 % ) . 