The most serious and important claim made by the appellants in these cases is that, without amendment of the complaints and against the defendants’ specific objection, the plaintiffs were allowed to prove and the jury to find that the boiler was defective in the' design and construction of its fire flue, whereas the defects charged in the complaints were defects and weaknesses resulting from wear and tear, improper use, and improper plugging of the safety valve.
It is very certain that this issue was litigated and passed upon by the jury in the Sellers Case. The first question of the special verdict in that ease submits this precise issue, and the jury answered it in the plaintiff’s favor; also by their answers to questions 7 and 8 in that case they found the use of the boiler with such defective design and construction to be negligence which was the proximate cause of Sellers’s death.
In the Brey Gase there is no direct question submitted to the jury as to defective design- or construction, but it seems *252certain tbat by tbe first question of tbe verdict, taken in connection witb tbe change of tbe court, tbe jury necessarily passed upon it. Tbat question, as will be seen by reference to tbe statement of facts, was as follows: “Was tbe boiler in question negligently kept by defendants in a dangerous and unsafe condition at and prior to tbe time of tbe accident ?”
Tbe instruction witb reference to tbis question was in part as follows:
“As to tbis question, you are instructed tbat if you are all satisfied to a reasonable certainty by a fair preponderance of tbe evidence tbat by reason of the construction and mainr tenance of tbe fire flue in tbat boiler, tbe defendants negligently kept tbe boiler in a dangerous and unsafe condition; or if you are all satisfied to a reasonable certainty by a 'fair preponderance of tbe evidence tbat by reason of tbe keeping of tbe globe valve, of wbicb you bave beard, in a closed condition prior to tbe accident, tbe defendants thereby negligently kept tbat boiler in a dangerous and unsafe condition, then and in either event you will answer tbis question ‘Yes,’ otherwise you must answer it ‘No.’ ”
By tbis question tbe attention of tbe jury was specifically called to tbe inquiry whether tbe boiler was unsafe and dangerous by reason of “construction and maintenance of tbe fire flue,” and they were in substance told tbat 'if it was tbe defendants were guilty of negligence. It seems tbat a juryman who believed tbat tbe fire flue was improperly constructed or designed was obliged to answer tbis question in tbe affirmative under tbe instructions, whatever might be bis conclusion witb reference to tbe condition of tbe globe valve. We conclude, therefore, notwithstanding tbe difference in tbe form of tbe questions, tbat the question of a defect in tbe design and construction of tbe fire flue was submitted to and passed upon by tbe jury in both cases, and forms one of tbe grounds of actionable negligence upon wbicb tbe conclusion of legal liability is based.
It is true tbat'in tbe Brey Case tbe jury found as a separate *253ground of negligence failure to warn the plaintiff of the likelihood of the boiler exploding by reason of its dangerous condition; but here again it seems inevitable that, if a juryman concluded that the boiler was unsafe by' reason of the defective construction of $he fire flue which the defendants ought to have known, that juryman must further have concluded that the failure to warn of this danger was the negligent failure to warn upon which liability rests in the Brey Case, and thus the question of the defective construction of the fire flue forms an inseparable part of the ground upon which liability is based under both verdicts. We therefore proceed to the question whether this question was properly in the case.
It is very clear to our minds from a mere inspection of the complaints that they do not charge any defect in the original design or construction of the boiler. We might consume considerable space perhaps in discussing this subject, but we should gain nothing thereby. If it appears to any mind that under any ordinary rule of construction such a defect is charged in the complaints we should not expect to be able to convince that mind to the contrary. This conclusion logically brings us to the question whether by reason of anything occurring on the trial of the case the question whether such a defect existed has become a proper subject of investigation and determination in the cases.
It seems that this could only be by reason of an amendment to the complaint made during the trial or at its close, or by reason of the fact that evidence bearing on the question was introduced without objection and thus the issue was litigated by consent of the parties without formal amendment of the pleadings. It is not claimed that there was any amendment of the complaints here, but that the defendants first introduced evidence affirmatively bearing on the question of design and construction, and thus opened the door and consented that the issue should be litigated.
*254In order to understand tbe basis of this claim it will be necessary to state some additional facts as well as some details of tbe trial.
Tbe dredging outfit was purchased by tbe defendants from a steam sbovel company in tbe early Jfart of tbe year 1907 and bad been in use two seasons and up to May 29, 1909. Tbe boiler was horizontal, round, about ten feet in length and fifty-four inches in diameter, having a round fire flue, which served as tbe furnace, twenty-nine inches in diameter, extending .from tbe front of tbe boiler about eight feet to tbe rear, ■and terminating in a combustion chamber which was separated from tbe rear end sheet of the boiler by a space of four or five inches, the combustion chamber being considerably larger than the fire flue. Eifty-four fire tubes or flues, two and one-half inches in diameter, extended from the combustion chamber above and at the side of the fire flue or furnace forward to the front of the boiler, thus bringing the smoke back to the smokestack. The fire flue and combustion chamber were completely surrounded by water when the boiler was properly operated. About midway in the length of the boiler was the steam dome, and out of it projected a two and one-half inch steam pipe carrying steam to the engine, also a one and one-half inch safety valve pipe extending through the roof, and intended to be furnished with the ordinary pop valve for safety purposes. There was a water glass and a steam gauge, and the pressure ordinarily carried was from 100 to 115 pounds. If the pressure went below ninety-five pounds the dredge would not operate as well as it should. Eor some reason — probably owing to the vibration of the scow — the pop valve or safety valve on the end of the last-named pipe was apt to become loose, and three or four such valves had been blown off by the pressure and became lost in the marsh, allowing all the steam to escape from the boiler and necessitating in each case a shut-down of several hours in order to get up steam pressure again. There is testimony *255that Sellers inserted a plug in the pipe after one of the pop valves blew off, thus closing it entirely. The last pop valve put on was arranged to go off at ninety-five pounds pressure, and at or before the time it was put on a globe valve was put on just below it, with the apparent idea that if the pop valve blew off the globe valve could be at once turned and thus prevent the boiler from being emptied of steam. It seems that Sellers or Kane put on the globe valve, but there is a dispute as to which did it. There is no doubt, however, that both knew of it. Either of them had authority to purchase such incidental repairs as were necessary and place them in position. Eor some days before the explosion the globe valve had been closed, and it was found closed after the explosion. Brey testified that he did not know the globe valve was there or that it was closed. He also testified that on the morning of the explosion he had raised the steam pressure to about ninety-five pounds, that he had a good fire on, and he proceeded to oil the machinery for about five or ten minutes, when the explosion took place. Ho one knows the pressure at the time of the explosion. The boiler was shot out of the scow by the force of the explosion and landed in the marsh some 500 feet distant.
The plaintiffs claimed that the explosion was caused by pressure of steam which the boiler in its weakened condition, with a closed escape valve, could not stand, while the defendants’ theory was that the explosion resulted because the water was 'allowed to become too low in the boiler by the fireman, Brey. The plaintiffs placed upon the witness stand two witnesses, l\ir. Henry J. Mistle and Prof. Mortimer Oooley, to give expert testimony as to the cause of the explosion after examination of the boiler. Both witnesses, after qualifying themselves to testify as expert engineers, testified that in their judgment the explosion was caused by excess of steam pressure, and that there was no evidence that it was caused by low water. Both witnesses based their conclusion principally *256upon the fact that the fire flue collapsed inward, indicating that the flue was compressed by the pressure of steam in the boiler around it. In the course of. Mr. Mistle’s direct examination he was asked: “You may state what the fact is with reference to the strength of this type of fire flue as compared with the ones now in general use,” and replied: “They are not fit for the high pressure they are carrying.” At this point the defendants’ counsel objected to the question on the ground that there was no issue in the pleadings as to the original construction of the boiler. Upon this objection argument was heard, and in course of the argument defendants’ counsel moved to strike out the answer which had been made. The court ruled with the defendants, and thereupon the plaintiffs moved for leave to amend the complaints so as to charge that the boiler was defective in type. On this motion being made, the defendants claimed that they were not ready to meet such an issue, and that-the cases would have to go over the term if the amendment were made. This statement was apparently received by court and counsel as sufficient without affidavit, and thereupon plaintiffs’counsel concluded that there was sufficient in the pleadings as they stood and he would not press the motion to amend. Mr. Mistle had stated without objection, just before the question above referred to was put, that the boiler was of an obsolete type, and the defendants’ attorney now moved to strike out all testimony as to the original condition or the type of the boiler, which motion was granted. These rulings we regard as strictly correct, and if the matter had stopped here the question before us never would have arisen. On Mr. Cooley’s examination, however, the situation changed somewhat. He stated his conclusion that the cause of the explosion was excess of pressure and not low water, and was then asked to point out to the jury what there was about the boiler which tended to support his conclusion, he being allowed to use some rough sketches which he had made to make the answers more clear. On objection be*257ing made to this form of examination because of the ease with which incompetent testimony might come in without opportunity for making objection, plaintiffs’ counsel said that the idea was to point out why the witness concluded that the explosion was due to high pressure and not to low water, and the court overruled the objection, saying that the witness was subject to interruption at any time if improper testimony appeared. The witness then proceeded without questions to explain the construction of the boiler at length, the character of the joints, the nature of the fractures made by the explosion, and generally all facts which he observed about the boiler and which he thought tended to support the conclusion that pressure of steam on the fire flue caused the explosion. In the course of his testimony the witness was asked whether there were any rings or other devices to reinforce the fire flue and replied in the negative, and further said that the flue was made of a single sheet. He had previously testified that the fire flue was constructed with lap joints, which have but seven tenths of the strength of butt joints, and all of these facts were apparently considered by the witness as facts tending to support his expert opinion that the explosion was the result of pressure of steam. Probably this testimony was admissible for the purpose for which it was offered, but because admissible for that purpose it cannot necessarily be considered as admissible for the purpose of proving an independent ground of liability not set forth in the pleadings, especially after the court had definitely ruled on that subject and the offer of the testimony was accompanied by the express statement that it was intended for the purpose of showing why the witness reached the conclusion that the explosion was due to steam pressure. We think that defendants’ counsel was entitled to rest upon the assurance that the testimony was offered 'and received for the one purpose stated, and not for the purpose of injecting into the case a new ground of liability to which he had so recently successfully objected. The testi*258mony being properly received, the defendants certainly bad full right to cross-examine on all matters gone into by the plaintiffs without forfeiting their right to have the action confined to the cause of action pleaded. It was expert testimony and its weight depended upon the qualifications of the expert, and it is well settled that an expert may be subjected to fairly exhaustive cross-examination upon subjects which legitimately throw light on his qualifications, such'as his education, the extent of his experience in practical application of his art or science, the extent of his observation outside of his own work, as well as other cognate matters bearing directly on his ability as an expert.
It was doubtless in reliance upon this principle that the defendants’ attorney upon cross-examination asked the witness questions concerning the supposed weakness in the construction of the fire flue, and particularly whether it was of unusual length, whether he ever saw a single-sheet fire flue of that length before, whether he considered it weak in construction, and if so how he would have constructed it in order to make it of greater strength.
All this seems to us to have been clearly legitimate cross-examination and not to have been examination upon a new subject, thus opening the door to an inquiry as to a new ground of liability not covered by the pleadings. Nevertheless, when plaintiffs’ counsel took the witness upon redirect examination, counsel for the plaintiff proceeded to ask the witness whether such fire flues were in general use and how long since they had been in general use, for the purpose of showing that the type had been obsolete for thirty years. Upon objection to this testimony the court ruled that by his cross-examination the defendants’ counsel had opened the door to testimony upon the general subject of the safe construction of such flues, and the witness was allowed to answer the questions and did answer them in effect as desired by the plaintiffs.
*259Thus the question of defective original construction of the fire flue was allowed to be brought into the case, and thereafter, as we have seen, the question was submitted to the jury, and the finding of the existence of such defect forms an inherent part of the ground of recovery in both actions which cannot be separated from the other grounds of liability found.
This court has gone -as far as any court, we believe, in disregarding mere defects of form in pleadings and in endeavoring to administer justice even when technical requirements-of pleading have not been followed, providing no substantial prejudice has resulted therefrom to the complaining party. McHolm v. Philadelphia & R. C. & I. Co. 147 Wis. 381, 132 N. W. 585. This is especially true where evidence has come in without objection. Hemenway v. Beecher, 139 Wis. 399, 121 N. W. 150; Swanby v. Northern State Bank, 150 Wis. 572, 137 N. W. 763. In the present case, however, there was timely and persistent objection to the introduction of any evidence concerning defects in original construction of the fire flue, as we have already seen. That objection was not waived by the cross-examination of the witness Cooley, and there is no room for holding that this question was ever tried by consent. It is very evident that the question of defects in original construction is a very important one. The defendants could not be expected to meet "that question in a day or perhaps in weeks. Counsel would not be justified in going to trial on that issue without considerable investigation, necessitating certainly the testimony of experts and perhaps the taking of depositions in other states. -
It seems apparent to us that the fundamental error which was committed by the court in allowing this new ground of liability to be litigated and submitted to the jury without amendment of the pleadings and without consent, either express or implied, must reverse the case. It must be considered to have affected the defendants’ substantial rights, namely, the right to know what charge of negligence is made *260against Mm in. time to make due preparations to meet it. Although, the testimony was taken and the objections and exceptions reserved in the Brey Gase alone, we regard the stipulation by which that testimony was to be considered in the Bellers Case with the same force and effect as if repeated in the latter case, as preserving the objections and exceptions in the Sellers Gase. Some other questions are raised, but as there must doubtless be amendment of the complaint 'and perhaps a considerable change in the issues presented, we do not feel obliged to discuss them now. For the reasons stated, there must be new trials in both cases.
By the Court. — Judgment reversed in each case, 'and action remanded for a new trial.
In the case of Brey v. Forrestal and another the following opinion was filed: