Adams, J.
Tbe foundation of legal liability for tbe creation or maintenance of a nuisance is ordinarily not so mucb tbe degree of care tbat is used as tbe degree of danger tbat exists even witb tbe best of care, while tbe ground of civil liability for negligence is injury to person or property when sucb injury is not tbe result of premeditation and formed intention. 20 R. C. L., 6. It is not essential to a disposition of tbe exceptions to decide wbetber tbe complaint should be regarded as based on one or both these grounds, for tbe theory adopted on tbe trial was tbe defendants’ negligent failure to perform a legal duty which they owed tbe plaintiff, and one of tbe main defenses was tbe insufficiency of tbe evidence'in any view to subject tbe defendants, or either of them, to any kind of legal liability. Tbis defense tbe appellants presented by a demurrer to tbe evidence or a motion for nonsuit. Whether tbe demurrer should have been sustained or tbe motion granted we are now to determine.
Tbe substance of tbe plaintiff’s allegations is set forth in -the statement of facts. For him it is contended in brief tbat tbe defendants’ failure to exercise due care in tbe construction and maintenance of their works and in tbe ponding of tbe water proximately caused tbe spread of tbe infection and brought about tbe plaintiff’s impaired health and anemic condition.
Several witnesses introduced as experts in medicine and sanitation expressed their opinion as to tbe types of malaria, tbe way in which it is contracted, its effects, and tbe means of prevention. Tbe scientific theory of causation, it was said, is a microscopic parasite injected into tbe blood by tbe bite of tbe Anopheles mosquito. It has been demonstrated, according to tbe testimony, tbat if a mosquito of tbis variety bite a person suffering from malaria, and after tbe parasite is devel[28]*28oped in tbe salivary gland bite a bealtby person, tbe latter will in due time develop malaria. Tbe converse also is true: persons wbo are protected from mosquito bites escape malaria. When tbis organism or parasite gets into tbe red corpuscles of tbe blood it develops into a larger organism wbicb breaks up into a number of parts, and in tbis way disrupts tbe corpuscles and turns tbe poison loose in tbe body.
There is evidence to tbe effect tbat of tbe three known malaria-bearing mosquitoes (Anopheles), only two are found in tbe region covered by tbe lake. These two are tbe Punctapennis and tbe Quadri-maculatus, benevolently abbreviated by tbe witnesses to “pune” and “quad.” There is further evidence tbat four things are essential to the production of the disease: the Andpheles mosquito, propagation, a person infected with tbe parasite, and a person wbo is well.
Tbis summary accentuates tbe pivotal question arising on tbe defendants’ demurrer to tbe evidence. They say tbat tbe Quadrimaculatus breeds in ponds and lakes and tbe Punctapennis along tbe banks of running streams and in small pools adjacent to streams where tbe water eddies; tbat both species bad been found along tbe ravines and streams now covered by tbe lake long before tbe water was impounded; tbat neither species has ever been found in tbe defendants’ lake or in any place connected with their works, and tbat tbe plaintiff was infected by mosquitoes tbat bad been propagated in streams and other natural breeding places entirely disconnected with tbe defendants’ property. Moreover, they contend tbat tbe disease was transmitted from infected laborers wbo bad come from malarial sections of the South to aid in tbe construction of tbe dams, and tbat tbe defendants, therefore, in no view of tbe evidence, caused or contributed to tbe outbreak of tbe malady.
On tbe other band, tb© plaintiff contends tbat up to tbe time tbe lake was built tbe whole community bad been free from malaria; tbat tbe first outbreak occurred in tbe summer of 1919 after tbe water bad been backed five or six miles up tb© coves and valleys; tbat sporadic cases of tbe disease previously occurring were traceable to tbe victim’s temporary sojourn in distant malarial regions; tbat before tbe water was ponded tbe Anopheles mosquito bad not propagated to an appreciable extent in tbat part of tbe State, but since tbat time both species have been found breeding along tbe margin of tbe lake and in pools of stagnant water left open by tbe defendants; that the importation of labor was a negligible and uncertain factor; tbat tbe Anopheles mosquito would not have bred on tbe lake if tbe banks bad been free from vegetation; tbat tbe defendant was negligent in failing to remove from the margin grass, vines, bushes, dead trees, and masses of second growth which protected tbe breeding places and in failing to drain or other[29]*29wise protect tbe small bodies of water standing in and near tbe old channels below tbe dams; and that as a proximate result of sueb negligence tbe plaintiff, bis wife, and tbeir children were infected with malaria and have suffered its attendant evils.
We find in tbe record evidence tending to sustain each of tbe inconsistent theories advanced by tbe respective parties. Under these circumstances, we need hardly repeat tbe legal truism that tbe plaintiff is entitled to tbe most favorable view of tbe evidence and to tbe benefit of any circumstances it tends'to establish, and that a demurer to tbe evidence or a motion for nonsuit can be sustained only when tbe evidence in no aspect is sufficient in law to warrant a verdict for tbe plaintiff. Tbe authorities to this effect are so numerous and so familiar as scarcely to call for citation. Allen v. Garibaldi, 187 N. C., 798; Hancock v. Southgate, 186 N. C., 278; Rush v. McPherson, 176 N. C., 562.
On behalf of tbe defendants it was argued that tbe plaintiff’s illness may have resulted from one of several causes, for some of which, at least, they were not responsible, and that tbe plaintiff must fail because tbe evidence does not trace bis ailment to tbe defendants’ negligence. In support of this position tbe defendants cite Rice v. R. R., 174 N. C., 268; Cobb v. Fogalman, 23 N. C., 441; Wittkowsky v. Wasson, 71 N. C., 451; S. v. Powell, 94 N. C., 965. But tbe plaintiff’s evidence, as indicated, was sufficient to carry tbe case to tbe jury and, if accepted, to warrant tbe verdict. His Honor, therefore, was correct in overruling tbe demurrer and declining to dismiss tbe action.
In tbe second group of assigned errors are exceptions to evidence tending to show that in 1922 and 1924 Anopheles mosquitoes were found to be breeding in tbe old bed of tbe Catawba River and at other places below tbe dams, and to tbe exhibition before tbe jury of a bucket of water dipped during tbe trial from places below tbe dams and, according to tbe plaintiff’s evidence, containing Anopheles larva. Tbe defendants assert there is no evidence that these places existed as possible sources of breeding in 1919 or that conditions then were similar to those prevailing in 1922 and 1924. But there is evidence'for tbe plaintiff tending to show that tbe condition of tbe old river bed was tbe same in 1922 as in 1919. Apart from this, however, tbe defendants contended throughout tbe trial, and repeat in tbeir brief, “that not a single Quadrimaculatus mosquito has ever been found breeding in tbe defendants’ lake or in any other place connected with tbe defendants’ works”; and upon this theory, as already suggested, they based one of tbeir principal defenses. This is shown from tbe cross-examination of witnesses introduced by tbe plaintiff prior to tbe time Fisher was called by tbe plaintiff for examination. Tbe first witness was Dr. Long, an [30]*30admitted medical expert, and on the cross-examination tbe defendants brought out evidence from which the jury might reasonably have inferred that, in his opinion, neither the dams nor the pools of water in the old channels had provided suitable breeding places for the malaria-bearing mosquito at any time. And so with others. Upon what ground should the plaintiff be denied the privilege of combating this theory before resting his case? It is au established principle that, while one substantive fact is not usually admissible to prove another, still, where an issue' is raised as to^ whether a given effect has been produced or can be produced by alleged causes, evidence apparently collateral is often admitted when the facts present such points of similarity as to afford reasonable data for a conclusion. Jones on Ev., sec. 164. But, without regard to this question, we learn from the record that the defendants in support of their theory offered witnesses 1 admitted to be experts who testified that they had examined the lake for mosquitoes in 1921 and 1922, and that, while mosquitoes bred profusely on the adjacent property, they were not found on the water of the lake. So said their witness, Dr. Carter; and Dr. Le Prince testified upon the trial that there were then no “quads” in the vicinity; from which he deduced the conclusion and expressed the opinion that none were there in 1919. The plaintiff introduced Mason, Hallyburton, and Jaynes in rebuttal. Unquestionably, their testimony was competent, and that of Fisher, even if otherwise inadmissible when offered, was also competent in com tradiction of the defendants’ witnesses afterward introduced. These assignments, we find, cannot be sustained.
The plaintiff propounded to Dr. Rankin two hypothetical questions which, together with the answers, are made the subject of the defendants’ fifth and sixth exceptions. Both questions are based upon an assumed finding of facts, the object of the first being to show the natural and probable effect of the existence of the assumed conditions upon the health of the community, and the object of the second to show whether the prevalence of malaria in the community might have been attributable to these conditions. The defendants urge two objections: (1) That the witness was permitted to express an opinion upon a vital question to be decided by the jury, and (2) that the questions assume the existence of facts which are irrelevant, immaterial, and unsupported by the evidence.
The last objection, it is true, must be considered in the light of decisions holding that it is error to admit a hypothetical question based on an assumed finding of irrelevant or unsupported facts. S. v. Holly, 155 N. C., 485; Bailey v. Winston, 157 N. C., 252; Dameron v. Lumber Co., 161 N. C., 495; Brewer v. Ring, 177 N. C., 476. But we do not admit the defendants’ premise that the hypothetical statement is either [31]*31irrelevant or unsupported. As to this objection, it will be seen that tbe questions clearly assume tbe conditions relied on as existing in tbe year 1919, wben tbe plaintiff was stricken, as well as in tbe two years next following; and if these conditions prevailed in 1919, whether or not they continued, would in no wise impair tbe strength of tbe plaintiff’s contention that they were a potent factor in producing bis illness. It was not incumbent on tbe plaintiff to include in bis questions all tbe evidence bearing upon tbe fact to be proved; tbe defendants bad tbe right to present other phases of tbe evidence in counter-hypothetical questions. S. v. Stewart, 156 N. C., 636; S. v. Holly, supra. Certain clauses in tbe questions are pointed out which tbe defendants insist have no basis in tbe evidence; but as we read tbe record there is evidence tending to support each of tbe clauses thus referred to. Those in tbe first question are abundantly sustained, and as to tbe clause in tbe second question particularly adverted to, it will be observed that tbe specific question was addressed to tbe “responsibility or degree of responsibility,” if any, of tbe assigned conditions, and tbe witness was unable to answer this question. No motion was made to strike out any part of bis explanatory remarks that may have been deemed unresponsive. Hodges v. Wilson, 165 N. C., 323; Wacksmuth v. R. R., 157 N. C., 34.
Tbe first objection also is without merit. In answer to tbe first question tbe witness expressed bis opinion upon a matter of science or skill in bis profession, not upon tbe existence or nonexistence of any ordinary circumstances to be determined exclusively by tbe jury. “There is a rule of evidence which excludes, on tbe ground of superfluity, testimony which speaks to tbe.jury on matters for which all tbe materials for judgment are already before tbe jury. This testimony is excluded simply because, being useless, it involves an unnecessary consumption of time and a cumbersome addition to tbe mass of testimony. In tbe majority of instances tbe testimony thus excluded will consist of an 'opinion’ by tbe witness — i.e., a judgment or inference from other facts, as premises, and it will be excluded because tbe other facts are already or may be brought sufficiently before tbe tribunal. If they are not or cannot be, then tbe witness’ judgment or inference will be listened to. Thus, it will often depend on tbe special qualifications of tbe witness whether be can add anything valuable which tbe jury have not already for themselves. "When, for example, tbe size and appearance of a skull-fracture has been testified to, tbe witness, if be is a person of only ordinary experience, cannot tell any better than tbe jury can whether tbe fracture is such as to have necessarily caused death; while, if be is a medical man, be is capable of adding considerably to the’ jury’s information on that point. In tbe former ease, bis judgment, or 'opinion,’ would be excluded; in tbe latter case, it would be listened to.” Wigmore [32]*32on Evidence, sec. 551. It is upon tbis principle that opinion evidence is admitted, but in admitting it the courts are vigilant to see that the province of the jury shall not be invaded, and to this end exclude, as far as possible, any inference or conclusion as to the ultimate fact in issue. Application of the rule is made in Nance v. R. R., 189 N. C., 638; Sill v. R. R., 186 N. C., 475; Smith v. Comrs., 176 N. C., 466; Kerner v. R. R., 170 N. C., 94; Mule Co. v. R. R., 160 N. C., 253; Deppe v. R. R., 154 N. C., 523. But it is not an inflexible rule, and it is frequently relaxed in the admission of evidence as to ultimate facts in regard to matters of science, art, or skill, as may be seen by reference to Holder v. Lumber Co., 161 N. C., 177; Ferebee v. R. R., 167 N. C., 290; Barrow v. Ins. Co., 169 N. C., 572; Moore v. Ins. Co., 173 N. C., 532, and to many other cases.
The vital question submitted do the jury on this phase of the evidence was embraced in the first issue, but the witness drew no inference from the testimony and merely expressed his professional opinion upon an assumed finding of facts by the jury. S. v. Bowman, 78 N. C., 509; S. v. Cole, 94 N. C., 958; Summerlin v. R. R., 133 N. C., 554; Brewer v. Ring, supra; Raulf v. Light Co., 176 N. C., 691. We must, therefore, overrule exceptions 5, 6, 8, ‘9, and 10, which are grouped under assignments 3 and 7.
The defendants called R. Y. Michaux as a witness and asked him this question: “Do you know of any cases of malaria up in that country (the Bridgewater section of Burke County) prior to the time the work was started on this dam?” The plaintiff’s objection was sustained on the ground that the question did not limit the area inquired of to one mile and a half of the plaintiff’s residence. The witness would have answered that he had personal knowledge of such cases. The defendants excepted to the exclusion of the evidence and to a similar ruling of the court in connection with the proposed testimony of other witnesses. These exceptions (15, 16, 17, 18, 20, 23, 24) are classed in assignments 4 and 8.
The defendants say this evidence was admissible as tending to disprove the facts assumed in the hypothetical question put to Dr. Rankin and to impeach the contention that the impounded water had caused the plaintiff’s illness. Under ordinary circumstances, the excluded evidence would have been competent (S. v. Hightower, 187 N. C., 300), but the question is whether the defendants are in position to take advantage of the exceptions.
After several of his witnesses had testified that malaria had never broken out in the community before the dams were built, the plaintiff offered to prove the condition of the lake, the old channels, and the Linville valley after the water had been impounded. The defendants [33]*33objected, and insisted that tbe evidence should be confined to conditions near the plaintiff’s dwelling. This objection and others of similar character were sustained. The' plaintiff afterwards called Dr. Houck, an expert witness, and asked him this question: “What would you say as to the prevalence of malaria during the period of your practice in Burke along the Catawba River in the section under consideration? Are you able to state whether malaria was prevalent in these valleys, in these sections, prior to the impounding of the water of Lake James?” The defendants objected unless the question were confined to a distance not exceeding one mile and a half from the place where the plaintiff lived — the distance which, according to all the evidence, is the radius of a mosquito’s.flight. This objection also was sustained, the plaintiff contending that he, therefore, had to abandon the further examination of the expert on whom he chiefly relied. After the defendants had thus circumscribed the plaintiff’s evidence, they excepted because the trial judge refused to relax in their favor and for their benefit the very rule they had invoked against the plaintiff. There is a marked similarity in the questions asked by the respective parties, and if incompetent for the plaintiff, the excluded evidence was likewise incompetent for the defendants. In fact, it is hardly probable that the defendants really hoped to destroy the ruling under which they had sought and secured protection. Greene v. Ruffin, 179 N. C., 345. Afterwards, however, they introduced other witnesses who testified that eases of malaria had been known there before the dams were built, and thus received the full benefit of this evidence. In our opinion, they have no just cause of complaint under these conditions.
The proposed testimony on behalf of the defendants that there was an' epidemic of malaria in Rutherford County in 1919 and none near a pond on Tom’s Creek, four or five miles from Lake James, was properly excluded. (Assignments 5, 6.) In what way it could have thrown any light on the controversy or aided the court or jury is not readily perceptible. It was entirely too remote. There is a fundamental postulate of evidence that circumstances which are irrelevant to the existence or nonexistence of the disputed facts are not admissible. The proposed testimony embodied neither an evidential nor an ultimate fact. Deming v. Gainey, 95 N. C., 528; Southerland v. R. R., 106 N. C., 100; Short v. Yelverton, 121 N. C., 95; Geer v. Water Co., 127 N. C., 349.
The plaintiff was permitted to prove by Dr. Butt, when recalled, that in June, 1924, he had found Anopheles mosquitoes near the upper end of the defendants’ lake and at other places more remote. (Exceptions 78, 91.) This evidence was admitted in rebuttal of Dr. Boldridge, who had previously testified as an expert for the defendants. He had said that in September, 1921, and again a year later he had made an investi[34]*34gation to determine whether mosquitoes would breed on Lake James; that malaria-bearing mosquitoes did not breed there in 1919; that he had come to this conclusion from his examination; that he had looked over the entire area of the lake and had yet to find his first “quad”; that the “pune” would not breed there — the former being a “pond breeder” and the latter a “stream breeder”; that he had examined practically all the streams or branches emptying into the lake and that virtually all seemed to be producing the “pune”; that he had examined the streams below the Catawba dam in the fall of 1922 and 1923, near the plaintiff’s house, and, in his opinion, mosquitoes were breeding there in 1919; that he had found pools along the old river bed, but that Anopheles mosquitoes would not breed in foul or .scum water, or in water containing iron in soluble form.
Eor the purpose of contradicting these statements, Dr. Butt was permitted to testify that he had found Anopheles mosquitoes breeding on the still waters of the lake and in the branches and other places; also that the water dipped by another witness from pools in the old river bed contained Anopheles larvse.
The defendants contend that the evidence should have been restricted to a compass of one mile and a half from the plaintiff’s house; but after the judge’s ruling on the question, Dr. Boldridge, at the instance of the defendants, testified that his investigation included the entire area of the lake and places outside or beyond it. If the evidence in chief was material for the defendants, was not the evidence in rebuttal material for the plaintiff ? So much of it as tended to show the finding of larvee in June, 1924, was admissible in contradiction of the defendants’ evidence that mosquitoes would not propagate where the larvse were found. "We are of opinion that the evidence excepted to was competent in contradiction of the defendants, if not competent in its relevant bearing upon the questions involved' in the first issue. Gaylord v. Respass, 92 N. C., 554; Clark v. Guano Co., 144 N. C., 64; Pool v. Anderson, 150 N. C., 624.
On 17 March, 1919, the plaintiff leased from the Western Carolina Power Company, one of the defendants, for a period ending on the first day of the following December, twenty-five acres of land situated a short distance below the Catawba, dam, “solely for agricultural purposes.” The lease contained the following agreement: “It is mutually agreed that the lessee shall take the premises subject to the right of the lessor to back or flood the waters of the Catawba and its tributaries upon said land hereby leased, and shall hold the lessor harmless from any and all claims or’ damages growing out of the backing or ponding of said waters, or the construction, maintenance, or operation of the dam or dams at or near Bridgewater. It is understood and agreed that. [35]*35tbe lessor shall have the right to enter and occupy all of said lands or any part of same at any time it may see fit, and that in case of such entry the lessor will pay to the lessee such actual damages as shall be caused to the crops of the lessee by reason of such entry or occupation.”
The trial judge instructed the jury as a matter of law that this agreement did not estop the plaintiff from prosecuting his action, and that the answer to the third issue should be “No.” The tenth assignment calls in question the accuracy of this instruction. (Exceptions 94, 96.)
The defendants contend that the plaintiff’s cause of action is for damages alleged to have been sustained by reason of their negligence in ponding and diverting the water of three streams; that it is, therefore, covered by the terms of the lease which stipulates against any and all claims growing out of the backing or ponding of the waters, and that they contracted with the plaintiff, not against negligence in the performance of a legal duty, but against the initial assumption of any such duty. To sustain this position the appellants cite a number of cases. Several of them simply enunciate the principle that in the absence of express stipulation the landlord is under no obligation to keep the leased premises in repair, but obviously these cases are not decisive of the point raised by the exceptions under consideration. Fields v. Ogburn, 178 N. C., 407; Improvement Co. v. Coley-Bardin, 156 N. C., 255; Duffy v. Hartsfield, 180 N. C., 151; Hudson v. Silk Co., 185 N. C., 342. In the other cases cited it is held in substance that a common carrier while performing its duties to the public cannot contract against its negligence, but if the public has no interest in the contract or in the property affected by it, such contract may not be void as against public policy. Slocumb v. R. R., 165 N. C., 338; Hartford Ins. Co. v. R. R., 175 U. S., 91, 44 Law Ed., 84; R. R. v. Voight, 176 U. S., 498, 44 Law Ed., 560; Robinson v. R. R., 237 U. S., 82, 59 Law Ed., 849; Wells-Fargo & Co. v. Taylor, 254 U. S., 175, 65 Law Ed., 205. In the first of these cases it appears that Slocumb leased from the railroad a strip of land on which he erected a building for business purposes; that the railroad constructed a siding on the leased premises for Slocumb’s use and benefit, and that it was agreed by the parties that any fire originating within the boundaries of the leased property should not be chargeable to the railroad. A spark escaped from a locomotive and started a fire which destroyed the lessee’s property. He brought suit and impeached the validity of the stipulation exempting the railroad from liability. In the case of the Hartford Insurance Company the circumstances were similar. In each case the question was whether the contract was against public policy. In the latter it is said: “The authorities all agree that a contract is not void as against public policy unless it is injurious to the interests of the public or contravenes some [36]*36established, interest of society. . . . The defendant owed no duty to tbe public to exercise care with respect to its own buildings situate on its right of way and incurred no liability for their negligent burning unless the fire spread beyond its own premises.” To the same effect is the decision in Sloeumb’s case, the Court approving Elliott’s statement, “We think that ordinarily a contract exempting a company from liability for negligently burning property not on the right of way or premises of the company would be held void.” In Voight’s case the question was whether he could avoid his agreement that the railroad company should not be responsible to him for injuries received while occupying an express car as a messenger by ifivoking the principle of public policy, which forbids a common carrier of passengers for hire to contract against responsibility for negligence; and it was held that he was not a passenger. In Robinson’s case and in Taylor’s practically the same principle was upheld.
We have reviewed these cases for the purpose of showing that they are not inconsistent with the instruction given in reference to the third issue. As we understand the lease, it involves neither public policy nor the right to contract; the agreement must be construed as it is written. The land was rented solely for agricultural purposes and the lessor reserved the right to enter and occupy all or a part of it at any time upon paying the lessee the actual damages done the crops by reason of such entry or occupation. The lessee took the land subject to the lessor’s right to flood it, and bound himself to pay the stipulated rent, notwithstanding injury to the land by flood or other external cause. Improvement Co. v. Coley-Bardin, supra. To forestall the lessor’s liability in case it caused damage to the leased premises by flood or otherwise, there was inserted in the agreement a clause exempting it from such liability by releasing all claims and damages, growing out of the ponding of the water or the construction, maintenance, or operation of the dams. So, construing the lease in its entirety, we think it manifest that the parties intended merely to provide against the lessor’s actual invasion by flood, entry, or otherwise, of the plaintiff’s possession or right of possession during the term of his lease, and did not contemplate the lessor’s exemption from liability for the creation outside the leased' premises of such unsanitary conditions as might result in a nuisance or might seriously impair the plaintiff’s health. To adopt the defendants’ construction of the agreement, we apprehend, would be equivalent to saying that in the construction of their works the defendants owed no duty to the public; but if 75 or 80 per cent of all-the people living in the community suffered in like manner with the plaintiff, as it is claimed, this fact would seem to indicate not only that the public was concerned, but that the agreement (under the decisions in the case of [37]*37Slocumb and in that of the Hartford Insurance Company) might- give rise to a serious question of public policy.
The plaintiff’s action is not based upon an actual invasion of bis possession or proprietary rights, creating a liability from which the lessor would be released by the agreement or upon the mere impounding of the water. It is based upon the negligent failure of the defendants to exercise due care with respect to the construction and maintenance of the lake for the protection of the plaintiff in the enjoyment of his legal rights. ■ The stipulated release, therefore, does not bar the present action, as his Honor correctly held, and for this reason, the exception to the directed instruction upon the third issue must be overruled.
We find
No error.