1. The defendant, under the provisions of St. 1913, c. 716, § 3, has moved for leave to amend its answer by setting up the defense that the plaintiff had assumed the risk of the accident that happened to him. We are of opinion that upon the facts of this case any such assumption of the risk must have been a contractual assumption of the open and obvious risks involved in the employment, and must have been made when the plaintiff entered upon the employment. It was not such an assumption as was considered in Leary v. William G. Webber Co. 210 Mass. 68; Flaherty v. New York Central & Hudson River Railroad, 211 Mass. 570; Lavartue v. Ely Lumber Co. 213 Mass. 65, 66; and Oswald v. Donohue, 215 Mass. 574. Here the question bears directly upon the duty owed by the defendant to the plaintiff, and comes under the doctrine that an employer is not bound to change the conditions manifestly existing when a contract of employment is made. Rivers v. Richards, 213 Mass. 515, 519, and cases there cited. It follows that the amendment is needless, and the motion is denied.
2. Coming to the merits of the case, the first question is whether there was evidence that this accident was caused by the negligence of the defendant. The plaintiff contends that while he was carrying a roll of cloth in the usual and proper manner over the spreader from the front to the rear of the machine, the speed of the machine was suddenly increased, and that the result of this increase was to throw the cloth over the pipe upon the shaft, so that it became caught there and wound around the shaft, and drew with it his hand and arm, and caused him serious injury. That is, the point which he makes is that the accident was due to the sudden increase of speed, in the first instance. As to this increase of speed, he makes two contentions. In the first place, *397he contends that the sudden and unexplained increase of speed in such a machine as this, while it is being operated in the usual and proper manner, comes under the same rule as the sudden and unexplained starting into motion from a position of rest of a machine which ought to remain still. In the latter case, it is now settled that such an occurrence, the sudden starting of a machine which ought to remain at rest, resulting in injury to one who has the right to suppose that it will remain still, comes under the rule of res ipso bquitur, and if unexplained affords evidence not only that there is a defect in the machine, but also that there has been negligence on the part of the employer who supplies the machine. Chiuccariello v. Campbell, 210 Mass. 532, in which some of the earlier cases are collected. Cook v. Newhall, 213 Mass. 392, 394, 395. The failure of an effort to stop a machine by the proper use of the apparatus provided for that purpose was held in Filosi v. Boston Woven Hose & Rubber Co. 214 Mass. 408, to come under the same rule. But in our opinion that rule ought not to be extended to cover a case like the one now presented. The rule itself, as was pointed out in Ryan v. Fall River Iron Works Co. 200 Mass. 188, 193, was established because “the court would not be justified in saying that the jury might not find, as men of experience in common affairs of life, that such a machine does not ordinarily start automatically without some negligence of omission or commission on the part of the employer, and that the existence of such negligence is the rational explanation of the starting.” But the case at bar in principle corresponds more nearly to Ridge v. Boston Elevated Railway, 213 Mass. 460, 462. This machine was operated by means of power transmitted to it through a system of shafting. Manifestly there were many influences which might vary or affect its speed, with more or less suddenness, and many of these influences would be wholly independent of any negligence on the part of the defendant. A change in the load put upon the main shaft by the stopping or starting of other machines to which power was transmitted from that shaft might at once cause a greater or smaller amount of power to be concentrated upon this machine and so accelerate or reduce its speed of operation. When it was first started, its speed naturally would increase until it had reached a maximum; and this increase might be, not regular or steady, but by a series *398of jerks or impulses, as the power supplied from the central source might be increased or as the load put thereon might be diminished. If this is left uncertain, in other words, if a sudden increase of speed is left unexplained, it might be due either to negligence for which the employer would be answerable, to the mere negligence of a fellow servant, or to the natural operation of proper machinery for which no one would be liable. Ragolsky v. Nurenberg, 211 Mass. 575. We are of opinion that the plaintiff cannot base a recovery upon this ground.
He contends further that there was evidence that the increase of speed and his resultant injury were due to a defective condition of the machine, and that this defective condition arose from negligence of the defendant. The increase of speed, he affirms, was due to a defective clutch, which had worn loose so that, as the bearings grew hotter and tended to come together, there was an increase of friction between them, power thus was transmitted more freely, and the speed of the machine “jumped up.” He contended also that the shaft by the side of the machine was not in a safe and proper condition for use on that kind of machine, because it had become "roughed up” in such a manner that something might catch on it and adhere to it and become twisted around it. That is, his contention is that the increase of speed was due to a defect in the apparatus provided by the defendant, that the effect of this speed naturally would be and actually was to throw the cloth forward and upon the shaft at the side of the machine; and that by reason of the roughened condition of the shaft the cloth was liable to be and actually was caught upon the shaft and drawn around it, carrying with it his hand and arm. There was also evidence that upon this shaft was a bearing fastened by a set screw, and that it was found afterwards that the slot in the head of this screw was “roughed up” at the sides, burred up slightly and more or less pointed. And the plaintiff contends that this was a defective condition, by reason whereof cloth thrown upon the shaft would be liable to be caught and drawn over the shaft, and that the jury might find that this was what did happen.
In support of these contentions the plaintiff relies mainly upon the testimony of one Forbes, called by the plaintiff as an expert witness. But on a careful examination of his testimony we cannot *399say that it indicates any actionable negligence on the part of the defendant. He testified, among other things, that the increased speed of the machine, if there was slack in front of the rolls, would pull the cloth up rather than throw it, would push it right along, would pile up the cloth in great loops as it fell over, that it (the cloth) would fall away from the roll; that if a speed of one hundred and fifty revolutions per minute pushed the cloth a foot away, a speed of sixty revolutions per minute would push it the same distance; that the speed had not much to do, had practically nothing to do, with the way the cloth would fall. There is no need of recapitulating the other testimony bearing upon this question. Looking at it all, we find nothing which would warrant the inference that the increase of speed had anything to do with the occurrence of the accident. If any negligence of the defendant was responsible for the increase of speed, it was negligence which did no harm to the plaintiff and cannot be made the ground of recovery.
As to the claim that the cloth was thrown upon the shaft, and caught upon it by reason of its roughened condition, the evidence excludes the hypothesis. We find no evidence that the speed of the shaft was greater than from forty to fifty revolutions per minute. According to Forbes’s testimony, the result of a speed of even sixty or one hundred and fifty revolutions per minute would be to push the cloth away from the machine only a foot. We find no evidence going further than this. But between the spreader roll and the steam pipes there was a space of eighteen or nineteen inches. Moreover, upon the testimony put in by the plaintiff he had gone, at the outside of the machine, to within six feet of its end. As the machine was eighteen feet long, he must have been about twelve feet from the spreader roll. If, as has been suggested, he was confused as to the ends of the machine, still his distance must have been six feet. There is no evidence that cloth could have been thrown such a distance, and it seems to us to be a physical impossibility.
The mere presence of the set screw upon the shaft, as the judge correctly said to the jury, was not material. It was a reasonable appliance, and the defendant owed to the plaintiff no duty to remove it. If however it had become so altered in its character, so roughened up by maltreatment or by misdirected efforts to *400test it or to tighten it as to involve a danger of cloth catching upon it, that might be a different thing. But apart from what already has been said about the shaft, upon the plaintiff’s own testimony and all the other evidence in the case, there is nothing to show that the cloth did become caught or entangled upon this screw. The plaintiff’s testimony as to the place where his arm was caught, the mark which he put upon the photograph which was in evidence, on the opposite side of the hanger from the set screw, and all the other evidence, indicate that the portion of the shaft around which the cloth was alleged to have been wound was between the hanger and the drum. And here again it may be added that upon the measurements stated to us we cannot see how the cloth could by any possibility have been thrown upon the screw.
We are constrained to say that upon all the evidence the plaintiff did not make out a case, and that a verdict should have been ordered for the defendant as it requested. Its exceptions must be sustained, and judgment in its favor must be entered.
So ordered.