126. " Contract of guarantee"," surety", principal debtor" and" creditor".- A" contract of guarantee" is a contract to perform the promise, or discharge the liability, of a third person in case of his default. The person who gives the guarantee is called the" surety"; the person in respect of whose default the guarantee is given is called the" principal debtor", and the person to whom the guarantee is given is called the" creditor". A guarantee may be either oral or written.