In making his claim the inventor is at liberty to choose his own form of expression, and while the courts may construe the same in view of the specifications and the state of the art, they may not add to or detract from the claim. And it is equally true that as the inventor is required to enumerate the elements of his claim, no one is an infringer of a combination claim unless he uses all the elements thereof. Shepard v. Carrigan, 116 U. S. 593, 597; Sutter v. Robinson, 119 U. S. 530, 541; McClain v. Ortmayer, 141 U. S. 419, 425; Wright v. Yuengling, 155 U. S. 47; Black Diamond Co. v. Excelsior Co., 156 U. S. 611, 617; Walker on Patents, $349. This principle is particularly important when we come to consider the "stationary card above the stretcher-bar," an element of the eighth claim.

The anticipating mechanism set up in this case is the socalled English Lake patent of October, 1881. This patent has been the subject of much adverse comment in the cases involving a consideration of it. And it appears to have lapsed for non-payment of taxes in June, 1885, and not to have been a successful machine. It may be the fact that the patent is not distinctly worded, and that the drawing and specifications are somewhat confused. It does appear, however, without contradiction in the record, that the machine now used by the respondents was made in a large measure from the drawings of the Lake patent. Mischke, one of the respondents, was put upon the stand by the petitioners, and testified that he made the changes in a short time from the Lake patent, which resulted in the alleged infringing machine. The Lake patent showed two brushes, whereas the respondents' machine has dispensed with one and changed the position of the other. He also admits to have changed the position of the cam and shortened the crank arm as shown in the Lake machine. It seems to be the position of the petitioners' expert that Mischke made the changes in the Lake patent necessary to convert it into an operative machine by adopting the controlling features of the Sutton patent. But whatever are the defects of the

Lake patent, the question here is, does the machine of the respondents infringe the eighth claim of the Sutton patent? One of the respondents' machines is in evidence and we have carefully examined it. Its general outline may be seen in the annexed copy of the photograph in evidence:

The operation of the alleged infringing machine is such that when the power is applied for moving the stretcher-bar it is carried forward to the revolving brush, and after the brush has separated the fur from the hair, carried upwardly, to be acted upon by the cutting knives. The reciprocating motion of the stretcher-bar from the brush to the knives is produced by the action of the crank (operating with the cam) on the main shaft, as shown in the photograph At the same time the mechanism for feeding the machine is in operation, actuated by the same application of power. This mechanism (shown in the photograph at the side of the respondents' machine) consists of the pawl (attached to the main frame) and the ratchet-wheel (attached to the moving frame), turning when the pawl engages therein, and acting with the worm gearing shown, to turn the roll which is part of the feeding mechanism. The operation is such that when the stretcher-bar is carried from the knives to the brush in the return motion, the action of the pawl upon the ratchet-wheel, with the worm gearing, causes the roll to turn and the pelt to be carried forward, the extent of the feed being regulated by the adjustment of the pawl. By this means the necessity of an independently acting mechanism for the feeding apparatus is avoided and the operation simplified.

The Sutton device, as we have seen, has a stationary stretcherbar; the respondents' mechanism has a movable stretcher-bar. The fixed stretcher-bar, about which the other mechanism acts, is made a distinct feature of the eighth claim. It is not present in the respondents' mechanism, unless it is true, as argued, that the one is substantially the equivalent of the other. It is said to make no difference whether the knife and brush are carried to the stretcher-bar or the stretcher-bar is carried to the knife and brush. This might be true if the mechanisms were substantially the same, and there was a mere transposition or substitution of parts. Such changes would amount to an infringement. But in determining infringement we are entitled to look at the practical operation

of the machines. The other elements of the eighth claim are to be used in connection with the apparatus shown in the Sutton patent, substantially as described. If the device of the respondents shows a substantially different mode of operation, even though the result of the operation of the machine remains the same, infringement is avoided. Brooks v. Fiske, 15 How. 212, 221; Union Steam Pump Co. v. Battle Creek Steam Pump Co., 104 Fed. Rep. 337, 343. In the latter case Judge Severens, who delivered the opinion of the court, after recognizing the doctrine that mere change of the location of parts, if the parts still perform the same function, did not take the structure without the bounds of the patent, said:

"If, however, such changes of size, form, or location effect a change in the principle or mode of operation such as breaks up the relation and coöperation of the parts, this results in such a change in the means as displaces the conception of the inventor, and takes the new structure outside of the patent."

And see Kokomo Fence Machine Co. v. Kitselman, 189 U. S. 8, in which case it was held that where the patent does not embody a primary invention, but only an improvement on the prior art, and the defendant's machines can be differentiated, the charge of infringement is not sustained.

In the case under consideration the respondents have dispensed with the fixed stretcher-bar and have adopted a movable one, operated by an entirely different mechanism, capable of accomplishing a much larger amount of work within a given time. In the Circuit Court of Appeals it was said to result in a double working capacity and product. It does not seem to us to be a mere transposition or substitution of parts; in the Sutton patent, the stretcher-bar being stationary, there are several mechanisms used for operating the movable brushes and the clipping knives; a different mechanism is used for operating the different parts which are to be brought to the fixed stretcher-bar in carrying out the operation intended. In the respondents' machine the same application of power moves the stretcher-bar and, by the coöperation of the feeding ap