Lorillian
The Lorillians were a humanoid species that could only breathe methyl oxide before the age of four. At that time, the mother had to wean her child off methyl oxide and onto oxygen. 

Commander Charles Tucker and Sub-Commander T'Pol encountered a mother/child pair of Lorillians on Rigel X in April of 2151. Tucker was shocked to see the child having breathing difficulties, and thought the mother was suffocating her child, until T'Pol gave him some insight into what the mother was doing to her child. ()

People 
 Unnamed Lorillians

External links 
 
 

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Species