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: Numerous periodic acid Schiff ( PAS ) positive , diastase resistant cytoplasmic inclusion bodies which appeared as myelin figures in cytosegresomes under the electron microscope were identified in the proximal convoluted tubules .
### Output Text:
Numerous <span class="chemical">periodic acid</span> Schiff ( PAS ) positive , diastase resistant cytoplasmic inclusion bodies which appeared as myelin figures in cytosegresomes under the electron microscope were identified in the proximal convoluted tubules . 