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 goal of these studies was to use an animal model to examine the effects of prenatal protein deprivation on behaviors and receptor binding with relevance to schizophrenia .
### Output Text:
The goal of these studies was to use an animal model to examine the effects of prenatal protein deprivation on behaviors and receptor binding with relevance to schizophrenia . 