Persons deaf and dumb may contract marriage, for they can give their consent by signs: 2 _Burn. Eccl. Law_, 415. _Swinb. s._ 15. 3 _Potier_, 165.[245] but it is essential, that they should be competent in all other respects, for there must always be a _prima facie_ suspicion that a person born deaf and dumb, by absence of the ordinary means of instruction, must be of imperfect capacity.[246] The third consideration is whether the parties are _habiles ad procreandos liberos_ in respect of corporeal ability, for that being the ultimate use and intention of marriage, the contract cannot be good unless the parties are in the condition of performing it;[247] except indeed where the incapacity arises from old age; _volenti non fit injuria_, and though neither the law of the land, nor the law of nature has, as far as it is known to us, prescribed any well-defined limit to the generative capacity,[248] yet after a certain period it may at least be so far doubtful as to create an implied waiver between the contracting parties.[249] Some foreign jurists and schoolmen have maintained, that the institution being solely _ad procreandos liberos_, it is a profanation of the rite to celebrate it between parties incapable;[250] but this doctrine is repelled by our liturgy, which even prescribes the omission of the prayer for procreation where the woman is past the age of childbearing;[251] how the priest is to ascertain this point we leave the civilians to determine. But a much more material question of medico-legal policy arises, as to the marriages of those who are afflicted with some serious hereditary disorder, or predisposition to disorder,[252] as _Scrofula_, _Mania_, &c.[253] in such cases public policy might induce an absolute prohibition,[254] but humanity would pause before it added this bann of excommunication to the misfortunes of its object; a middle course might be adopted: Mahon[255] says that the Protestant church admits epilepsy as a good cause of divorce, and that _Alberti_ has handed down a decision of the faculty of Halle on this subject; we do not know any English case on the point, and very much doubt whether our ecclesiastical courts would admit the principle; unless indeed it were made out, that the disorder constituted a moral impotence, or that one of the parties could not perform the contract but at the risk of life.