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 cell populations were examined regarding total cell recovery correlated with gland weight , intracellular prolactin ( PRL ) content and subsequent release in primary culture , immunocytochemical PRL staining , density and / or size alterations via separation on Ficoll - Hypaque and by unit gravity sedimentation , and cell cycle analysis , after acriflavine DNA staining , by laser flow cytometry .
### Output Text:
The cell populations were examined regarding total cell recovery correlated with gland weight , intracellular prolactin ( PRL ) content and subsequent release in primary culture , immunocytochemical PRL staining , density and / or size alterations via separation on Ficoll - Hypaque and by unit gravity sedimentation , and cell cycle analysis , after <span class="chemical">acriflavine</span> DNA staining , by laser flow cytometry . 