the defendant has personal knowledge of the record which he pleads, and can therefore make the required oath that there is in fact such a record. If he has no such knowledge, the defence must be made in an answer, for the ancient rule that records may be pleaded in equity, without an oath, is inconsistent with the United States equity rule upon the subject of pleas.' § 615. The twentieth defence can be made by a demurrer, where the bill shows the patent to have expired when the doings which constitute the alleged infringement were committed. But that will seldom be the fact, for the expiration relied upon in such cases is nearly always due to the expiration of some foreign patent for the same invention, and not to anything which appears on the face of the United States patent in suit. Where the defence depends upon the expiration of a foreign patent which is not mentioned in the bill, it cannot be set up in a demurrer. Nor can it always be set up in a plea, because it depends not only upon the existence of a foreign patent, but also upon that patent being for the same invention as the patent in suit, and because this last question, except where the two patents are plainly identical, is one of construction for the court. This defence must therefore generally be interposed in an answer. 3 § 616. The twenty-first defence may be made in a plea, if the defendant knows that the complainant made or sold specimens of the patented thing during the life of the patent without marking them "patented," and if the defendant was not duly notified of his infringement, or, if notified, immediately discontinued to infringe. This defence can also be made in an answer, and that is the most convenient pleading in which to interpose it, because it is seldom a full defence to an action in equity. It is never a defence to a prayer for an injunction, though it is to a prayer for damages. 1 Equity Rule 31. Whether it is a defence to a prayer ? De Florez v. Reynolds, 17 Blatch. 436, 1880. Revised Statutes, Section 4900. 1868. for infringer's profits, is an unsettled question, the solution of which will involve the balancing of a number of considerations. In the affirmative, it can be argued that profits are but equitable substitutes for damages, and as equity follows the law in respect of other parts of the patent system, it ought also to follow it in this. But it can be replied in the negative, that equity does not altogether follow the law in the matter of pecuniary recoveries for infringements of patents, but primarily determines the amounts of such recoveries on quite different principles from those used in courts of law for that purpose. And it can also be argued in the negative, that though it would be wrong to force a defendant to pay damages, regardless of the amount of his profits, for infringements against which the complainant neglected to warn him, it would not be unjust to compel a defendant to return to the complainant whatever profits the former realized from even an unwitting infringement of the patent of the latter. To this last point it can be rejoined for the affirmative, that such a case is not merely a case of unwitting infringement, but is also an instance of a patentee leading others to infringe his patent, by unlawfully concealing the fact of its existence, and that, though a failure to mark "patented" would lack some of the elements of a technical estoppel, still it is such a violation of the statute as ought to cause a forfeiture of all remedies for infringement committed before the giving of actual notice of the patent. § 617. The twenty-second defence may be made by demurrer, where the bill sets forth copies of the complainant's title papers, either in the stating part, or in exhibits attached to the bill and thus made parts thereof, or where the bill pleads those papers according to their legal effect, and in such a way that the title appears on the face of the bill to be defective. Where the bill shows a good prima facie title, but where the defendant knows that one of the papers which compose its chain was executed after the assignor had assigned his right to another, and that the prior assignment was recorded in the Patent Office within three months after its date; or knows that such assignor assigned his right to another for a valuable consideration, more than three months after the making of the assignment set up in the bill, and before the latter was recorded in the Patent Office, and without the junior assignee having notice of the senior unrecorded assignment; the defendant may successfully set up those facts in a plea. The action of a complainant will be defeated by evidence of either of these two sorts of faults in his title.' Either of these sets of facts may also be set up in an answer, but it is better to interpose them in a plea when the defendant is certain of their existence. § 618. The twenty-third defence may be put into a plea, and that is the most appropriate pleading in which to interpose it, where the defendant is sure of the fact of a license. But if there is any doubt about the existence of a vital license, and if the defendant has any other defence, it is unwise to trust the case to a plea, for if he fails in proving its truth, he will thereupon suffer final defeat, no matter how many other defences he might have invoked. § 619. The twenty-fourth defence should be treated in respect of pleading in the same way as the twenty-third, and that whether the release pleaded, was executed before or after the filing of the bill.' $620. The twenty-fifth defence may be interposed in a plea, but there is no good reason for adopting that practice, and there is an excellent one for avoiding it. When such a plea is put in, the complainant has no alternative but to file a replication, because non-infringement is undeniably a perfect defence to a bill based on alleged infringement of a patent. Such a replication will confine the issues of the case to the single one of infringement,' and thus cut off all other defences, if that issue is decided against the defend 1 Revised Statutes, Section 4898. ? Daniell's Chancery Practice, 669. 3 Hughes v. Blake, 6 Wheaton, 472, 1821; Rhode Island v. Massachusetts, 14 Peters, 257, 1840; Myers v. Dorr, 13 Blatch. 26, 1870; Story's Equity Pleading, Section 697; Daniell's Chancery Practice, Vol. 1, Ch. XV. Sec. V. ant. It was a disregard of these points of equity pleading, that led, in two cases on the circuit, to holding that a plea of non-infringement is not admissible in an equity suit.' Where the defendant is sure that he has never infringed the patent upon which he is sued, a plea of non-infringement is the scientifically correct defence to make. But if he has any doubt on that point, and has any hope based on any other defence, he should not risk the entire litigation on one issue should not plead non-infringement, but should set up that and all his other defences in an answer. § 621. The twenty-sixth defence may be made in a plea, and it ought to be so made in every case where the defendant is certain that he can prove the facts which he is advised amount to a basis for an estoppel. If those facts are found, on an argument of the plea, not to constitute an estoppel, the defendant will be permitted to file an answer setting up other defences. It is only when a plea in equity is replied to, and then proved not to be true in fact, that a defendant loses any proper advantage by filing such a plea. § 622. The twenty-seventh defence may be interposed by a demurrer, where the bill clearly states the time when the infringement was committed, or the space of time during which it was carried on. Where the bill simply states that the infringement occurred during the life of the patent, and where any part of that life is remote enough in point of time to be barred by either the national or the State statute of limitation, if either is applicable thereto; then the applicable statute must be set up in a plea or in an answer, in order to avail the defendant. An answer is to be preferred to a plea for this purpose, in all cases where the statute bars only a part of the right upon which the action is based; because an answer must generally be filed to the residue of the bill, and because the proceedings are simplified by putting all the defences into one pleading. 1 Mitford & Tyler's Equity Pleading, 390; Theberath v. Trimming Co. 5 Bann. & Ard. 585, 1880. Sharp v. Reissner, 9 Fed. Rep. 445, 1881; Korn v. Wiebusch, 33 Fed. Rep. 51, 1887. Statutes of limitation have the same effect upon actions in equity in the Federal courts, that they have upon corresponding actions at law.' § 623. A replication is required to be filed by the complainant, in order to put in issue those points wherein the answer disagrees with the bill. No special replication is permitted in equity in the United States courts. The general replication is required to be filed on or before the rule day, which next succeeds that upon which the answer is due and is filed; but if filed after that time, it may, at the discretion of the court, be ordered to stand; or it may, if offered after that time, be allowed by the court to be filed nunc pro tunc as of the day whereon it was due.' § 624. Before tracing further the common course of an action in equity for infringement of a patent, it is expedient to make a short excursion into the field of those subordinate bills which are sometimes required to be filed, before decrees for infringements can properly be entered. Four kinds of such bills are known: 1. Supplemental bills. 2. Bills in the nature of supplemental bills. 3. Bills of revivor. 4. Bills in the nature of bills of revivor. § 625. A supplemental bill is required, where the original bill was filed by a person as executor or administrator, or as assignee in bankruptcy or insolvency, whenever any other person succeeds to the title of the complainant to act in that representative capacity. Such a bill is also necessary, in order to subject the estate of the defendant to a decree, where he is adjudged bankrupt or insolvent after the bill against him is filed.' His assignee in bankruptcy or insolvency is the proper person to be made the defend |