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: The mean body weight of dogs with grade 4 neutropenia ( 19 . 7 kg + 13 . 4 kg ) was significantly less than the mean body weight of dogs that did not develop grade 4 neutropenia ( 31 . 7 kg + 12 . 4 kg ; P = . 005 ) .
### Output Text:
The mean body weight of dogs with grade 4 neutropenia ( 19 . 7 kg + 13 . 4 kg ) was significantly less than the mean body weight of dogs that did not develop grade 4 neutropenia ( 31 . 7 kg + 12 . 4 kg ; P = . 005 ) . 