1. When Kalkapa obtained from Sidoji the mortgage for Rs. 6,000 on which he now sues (No. 3, dated 6th February 1873), the mortgage of 1869 to Basalinga, representing Parapa, was still unsatisfied. It is referred to in exhibit No. 3, and the money, it is recited, is borrowed in part for the purpose of paying it off. Parapa subsequently, suing Sidoji to enforce his earlier lien, obtained a decree for possession on the 10th November 1873, under which he was put into possession on the 22nd December 1873.
2. Kalkapa has now come forward seeking possession on his mortgage; and he says that the decree in favour of Parapa was obtained by collusion with Sidoji, Parapa's claim having, in fact, been satisfied by an intermediate transaction of the 18th June 1873. To establish this transaction, Kalkapa put in evidence a document (No. 45) called a receipt, but intended, if authentic, to entirely release Parapa's claim, through Basalinga, under the mortgage of 1869. This instrument seems not to have been objected to below on the ground of its nonregistration; but that objection having been taken before us, we have to consider whether it is open to the defendant Parapa at this stage, and whether it must be admitted so as to exclude the document as evidence to be made use of in disposing of the case. On the first point we are of opinion that we are bound to take notice, in regular appeal, of a positive invalidity of a document created by a statute, even though no objection may have been raised to its admission in the Court below. In the case of Nixon v. The Albion Marine Insurance Company L.R. 2 Ex. 338, the Court declined to proceed on a case submitted to it, the document on which the claim rested being unstamped, though both parties were desirous of a decision. The interests of the revenue, the Court thought, required that they should, suo motu, notice the defect which came under, their observation in the course of the inquiry. The bulwark against fraud, intended to be constituted by registration, is of as great public importance even as the interests of the revenue, and when we find that the Registration Act VIII of 1871, Section 49, says not only that a document requiring registration, but unregistered, shall not be received in evidence, but also that it shall not affect any immoveable property, we think that we could not, consistently with the law, allow it to count as a part of the materials on which we have to dispose of this case, supposing that registration was, indeed, indispensable to its validity.
3. On that point it has been urged by Mr. Mandlik that the document No. 45 is, prima facie, a receipt that his client Kalkapa wishes to employ it in no other character, and that as a receipt it did need registration. But as a mere receipt for so much money, if it were in truth limited to that, it could not prove the release or extinguishment of any particular right over the property in dispute vested in Parapa by the mortgage. It could not, therefore, show that, in subsequently admitting Parapa's claim under that mortgage, Sidoji wilfully failed to assert his own rights. It was only if his mortgage was released that Parapa's claim to possession could be unfounded, or Sidoji's admission of it could be a fraud on Kalkapa. To prove that it had been released, the document No. 45, which is express to that effect, was put in and that is exactly the use that was made of the document by the Subordinate Judge. In the case of exp. Mackay L.R. 8 Ch. App. 643 Mellish, L.J., says of an agreement to execute a bill of sale: 'No doubt, qua agreement, it does not require registration; but, in my opinion we ought to hold that an agreement to execute a bill of sale ought not to be held equivalent to an actual bill of sale in equity without involving the consequence that brings it within the Bills of Sale Act, and that, if it is not registered, the Court will look on it as invalid.' This was fallowed in exp. Conning L.R. 16 Eq. 414, and it is clear that the design of the Registration Acts would be entirely defeated if a document, introduced as of a kind not requiring registration, could then forthwith be employed for purposes which the law intends to be effected only by registered instruments. The observation of Lord COTTENHAM in Evans v. Prothero 20 L.J. Ch. 456.' shows that, in his opinion, a document which required a receipt stamp, could not be used unstamped to prove either the payment of the money as an ultimate fact, or any remoter matter towards the proof of which the payment of the money would tend by way of inference. In a subsequent stage of the same case Lord ST. LEONARDS (21L.J. Ch. 772) thought that, as evidence of an agreement referred to in it, the document would be admissible, but this would have been independently of the sense of the document as a receipt, and through words separable from those which constituted the acknowledgment. In the case, now before us the document No. 45 can have made the subsequent suit and admission collusive only by operating as an actual release; and operating or being meant to operate in that way, it required registration.
4. The case of Futtehchund Sahoo v. Leelumber Singh 14 Moor Ind. Ap: 129 strongly supports the view we take of this case. There an instrument acknowledging the receipt of money as consideration, not for an absolute conveyance, but for an agreement to execute a conveyance was held by the Judicial Committee, under circumstances of considerable hardship, to be inadmissible without registration as evidence of the transaction recorded in it. To the same effect is the case of Valaji v. Thomas I.L.R. 1 Bom. 191, and (Mahadaji v. Vyankaji I.L.E. 1 Bom. 197 is closely parallel to the present case. Westropp, C.J., says: ''The object of the first defendant (appellant) in giving the instrument No. 17 in evidence, is to show that Kazi Muhammad's mortgage lien  on the land has been extinguished, and was so previously to the alleged transfer or assignment of that lien to the plaintiff'; and as the acknowledgment would have this operation, and it was proposed to use it for that purpose, the learned Chief Justice said that it was clearly 'inadmissible for such a purpose.' Although, therefore, the document No. 45 might conceivably be admissible for some purposes, it cannot, we think, be used to establish the fact which it was brought forward to prove; and the basis, on Which the allegation of fraud and collusion rested, thus seems to us entirely to fail.
5. It is said, however, that the plaintiffs, had this document No. 45 not been admitted in the Court below, might have proved the alleged collusion by other testimony, and that they ought now to have an opportunity of bringing forward that testimony if it be procurable. But the charge against Parapa and Sidoji was one of collusion to defeat Kalkapa's mortgage lien, by a specified means, namely, the fraudulent withholding, by Sidoji, of the good defence which the document No. 45 afforded to him against Parapa's suit on his mortgage. If there was any other ground than this particular collusion on which Kalkapa's claim could be rested, he was bound to bring it forward: resting on the alleged collusion, he was bound to bring forward all the evidence of it that he thought might strengthen his case. A good deal of such evidence he has,. in fact, brought forward, and we cannot doubt that if he had found additional, testimony available, he would have made use of it. But we do not think, that when a portion of the available evidence has been neglected by a party in reliance on a 'particular document, not in itself decisive of the issue, but only affording strong evidence bearing upon it, he can reasonably claim that this defect of judgment on his part should be remedied by a new 'trial of the same issue. The document No. 5 in this case, even if proved, was not. necessarily decisive of the issue of collusion; the conduct of Parapa and Sidoji might admit of explanation; and Kalkapa ought to have' brought forward, as, indeed he probably did, all the confirmatory evidence that could be had. We. Cannot, therefore, remand the case; and as it is hardly contended that the decision of the Subordinate Judge can be supported on the evidence as it stands, we must reverse it, and reject the claim, with costs in both Courts on the plaintiffs.