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: One week later , they received repeatedly vehicles ( saline , DMSO , saline + DMSO ) , scopolamine ( 2 microg / 0 . 5 microl saline / side ; 30 min before training ) , ritanserin ( 2 , 4 and 8 microg / 0 . 5 microl DMSO / side ; 20 min before training ) and scopolamine ( 2 microg / 0 . 5 microl ; 30 min before ritanserin injection ) + ritanserin ( 4 microg / 0 . 5 microl DMSO ) through cannulae each day .
### Output Text:
One week later , they received repeatedly vehicles ( saline , <span class="chemical">DMSO</span> , saline + <span class="chemical">DMSO</span> ) , <span class="chemical">scopolamine</span> ( 2 microg / 0 . 5 microl saline / side ; 30 min before training ) , <span class="chemical">ritanserin</span> ( 2 , 4 and 8 microg / 0 . 5 microl <span class="chemical">DMSO</span> / side ; 20 min before training ) and <span class="chemical">scopolamine</span> ( 2 microg / 0 . 5 microl ; 30 min before <span class="chemical">ritanserin</span> injection ) + <span class="chemical">ritanserin</span> ( 4 microg / 0 . 5 microl <span class="chemical">DMSO</span> ) through cannulae each day . 