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 50 % effective dose of d - tubocurarine ( microg / kg ) in the tibialis muscle was smaller in the P10 ( 33 . 6 + / - 5 . 4 ) than in the S ( 61 . 9 + / - 5 . 0 ) or the P100 ( 71 . 3 + / - 9 . 6 ) groups .
### Output Text:
The 50 % effective dose of <span class="chemical">d - tubocurarine</span> ( microg / kg ) in the tibialis muscle was smaller in the P10 ( 33 . 6 + / - 5 . 4 ) than in the S ( 61 . 9 + / - 5 . 0 ) or the P100 ( 71 . 3 + / - 9 . 6 ) groups . 