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 yield of severe cirrhosis of the liver ( defined as a shrunken finely nodular liver with micronodular histology , ascites greater than 30 ml , plasma albumin less than 2 . 2 g / dl , splenomegaly 2 - 3 times normal , and testicular atrophy approximately half normal weight ) after 12 doses of carbon tetrachloride given intragastrically in the phenobarbitone - primed rat was increased from 25 % to 56 % by giving the initial " calibrating " dose of carbon tetrachloride at the peak of the phenobarbitone - induced enlargement of the liver .
### Output Text:
The yield of severe cirrhosis of the liver ( defined as a shrunken finely nodular liver with micronodular histology , ascites greater than 30 ml , plasma albumin less than 2 . 2 g / dl , splenomegaly 2 - 3 times normal , and testicular atrophy approximately half normal weight ) after 12 doses of <span class="chemical">carbon tetrachloride</span> given intragastrically in the <span class="chemical">phenobarbitone</span> - primed rat was increased from 25 % to 56 % by giving the initial " calibrating " dose of <span class="chemical">carbon tetrachloride</span> at the peak of the <span class="chemical">phenobarbitone</span> - induced enlargement of the liver . 