Opinion by

If the finding of facts made by the court below can be sustained the decree was appropriately entered and we are not persuaded that the court was in error in this respect. The case does not depend on the uncorroborated evidence of the plaintiff for it is conceded that the assignment of the building and loan association stock was made in the first instance as collateral security for the payment of the loan of $2,400 obtained by the defendant *309for Charles A. Berger, and it is also admitted that this loan was paid in the lifetime of the decedent. In the absence of evidence that the stock was transferred to the defendant in satisfaction of a loan the assignment is presumed to be collateral security for the debt. The transaction did not amount to payment. It gave to the creditor additional means of making himself whole, but if the stock proved to be valueless the debtor continued liable on his personal obligation: Perit et al. v. Pittsfield et al., 5 Rawle, 166; Stone v. Miller, 16 Pa. 450. There is no evidence that the decedent was indebted to his father for more than the $2,400 at the time the assignment of September 23 was made, and this assignment is consistent with the agreement of September 4, 1907. William Berger recognized the collateral character of the latter document. He did not procure a new certificate of stock for the shares assigned by his son until after the death of the latter, and apparently intended to hold the stock with the relation thereto which the contract of September 4 created. The argument that the answer is not overcome.by the plaintiff’s evidence loses its weight when we consider that the defendant sets up a new contract not pleaded by the appellee and made subsequently to the transaction set forth in the bill. That an answer responsive to the plaintiff’s bill is conclusive in favor of the defendant unless it is overcome by the satisfactory testimony of two witnesses or of one witness corroborated by other facts which give it greater weight than the answer or which are equivalent in weight to two witnesses is well understood, but it is equally well determined that another subsequent, independent and distinct fact not stated in the bill is not responsive and therefore not within the rule. Whatever constitutes a part of the facts stated in the bill the defendant should set out, but while thus becoming a witness for the plaintiff he cannot testify for himself and introduce other facts by way of defense or avoidance. Where a different contract is set up by the defendant and which is alleged to have superseded the one charged by the plain*310tiff the defendant has the affirmative of the issue on the allegation as to the subsequent matters, and must make proof: Pusey et al. v. Wright et al., 31 Pa. 387; Eaton’s Appeal, 66 Pa. 483. The averment contained in the answer that the defendant Berger bought the stock from his son and paid therefor at a time subsequent to the mattexs set up in the plaintiff’s bill is pleaded by way of defense and avoidance. It is claimed that this later transaction set aside the pledge and vested in Wm. Berger absolute title to the stock. This was a distinct transaction not involved in the case as made up by the plaintiff and one with reference to which the defendant must offer proof if he seek to avail himself of it. It is not a responsive averment within the rule regulating the effect of an answer in equity. The court was not in error, therefore, in holding that there was no proof of other loans by Wm. Berger than $2,400 and $350.

We regard the question of the competency of Mrs. Berger to testify in favor of her husband as settled in Bitner v. Boone, 128 Pa. 567, and Myers v. Litts, 195 Pa. 595. The disability of husband or wife to testify in favor of the other is based in part on the identity of the interests of the husband and wife and in part on considerations of public policy which hold it to be necessary in order to promote the harmony of the domestic relation and the confidence of private life. In any view of the case Mrs. Berger was not competent to testify.

The decree is affirmed.