If the answer will tend merely to disgrace but not to incriminate the witness, the privilege does not apply. If, however, the answer is one which can have no bearing upon the case except to impair the credibility of the witness, he may refuse to answer.69
The immunity which is provided has for its object the protection of the individual against criminal prosecution based upon evidence which has been compulsorily obtained from him. Thus the provision is no bar to the use in a subsequent prosecution of evidence that has been voluntarily given by the accused; nor does it prevent the courts from compelling testimony with reference to acts no longer punishable, or where, by statute, subsequent use of the evidence so obtained in criminal actions has been forbidden. Thus also the immunity does not relate to evidence the tendency of which is merely to discredit the moral character of the witness.70
In Hale v. Henkel71 the court declare the broad doctrine that the line is drawn at testimony that may expose the witness to criminal prosecution. "If the testimony relate to criminal acts long since past, and against the prosecution of which the statute of limitations has run, or for which he has already received a pardon, or is guaranteed an immunity, the amendment does not apply. . . . The criminality provided against is a present, not a past criminality, which lingers only as a memory, and involves no present danger of prosecution."