Opinion by

James Dottling, a minor son of the plaintiff, was killed while performing services in the employ of the defendants; his mother sued in trespass, alleging negligence, and recovered a verdict of $2,238.05, which subsequently was reduced to $1,600. Judgment was entered accordingly, and the defendants have appealed, contending: (1) “The negligence which plaintiff imputes to defendants was not the proximate cause of the injury”; (2) “The boy for whose death the plaintiff claims was guilty of contributory negligence”; and (3) “The plaintiff did not submit any sufficient evidence from which a verdict in her favor could be rendered.”

When the evidence is viewed in the light most favorable to the plaintiff, as it must be, since the verdict was in her favor, these material facts appear: The defendants owned and operated a coke plant; at the time of the accident James Dottling was working at a conveyor used for the purpose of carrying coke ashes from the coke yard up an incline to a boiler house; in performing this work he was obliged to stand upon an insecure plank ten or twelve inches wide and seven or eight feet long at an elevation above the ground, or in another equally unsafe position; the belt of the conveyor was propelled by a revolving drum; at times the belt would slip in such a manner that it would cease to move; when this occurred it was customary for one performing the duties at which Dottling was engaged to use upon the' belt a preparation furnished by the defendants consisting of tar and some other substances; the preparation was customarily applied while the belt was running; Dottling was performing his usual duties, in closé proximity to a series of cog-wheels, which were neither fenced nor guarded as required by the acts of assembly in Pennsylvania, the belt was slipping and he was applying this tar solution, when his hand caught; he was drawn into the cógs and so severely injured that very shortly thereafter he died.

*450The issues were left to the jury; they found the defendants were negligent in not guarding the cog-wheels, that this was the proximate cause of the accident, and further, that the injured lad was not guilty of contributory negligence. The plaintiff established a prima facie case by proving defendants had failed to guard the cogs, and that her son was killed by coming in contact with them while engaged at his customary work. The failure to guard these cog-wheels was a neglect of statutory duty from the consequences of which nothing but the contributory negligence of the employee would relieve the defendants, and whether or not the plaintiff’s son was guilty of contributory negligence was clearly an issue for the jury, not for the court (Bollinger v. Crystal Sand Co., 232 Pa. 636, 638). It is true the plaintiff produced no positive evidence that the injured lad had been expressly instructed to place the preparation upon the belt, but there was ample proof that this was the customary and permitted practice pursued by those engaged at the particular work he was performing, if occasion so required (see Fortney v. Breon, 245 Pa. 47, 52, 54). No one actually saw the happening of the accident, and the plaintiff was entitled to the presumption that her son exercised ordinary care (Smith v. Stoner, 243 Pa. 57). More th an this, many of the witnesses described the lay of the injured lad’s body when it was found entangled in the cogs, the position of his hand and arm, and gave physical illustrations; and, since there is no description upon the record of what these illustrations indicated, we must assume that they went to support the verdict (Wagner v. Standard Sanitary M’f’g. Co. 244 Pa. 310, 316; Fortney v. Breon, supra, p. 53).

On the last point, the appellants contend that there was no sufficient evidence produced by the plaintiff to show how much it would have cost to maintain her son between the time of his death and the date of his majority, and hence, that the proofs were insufficient to justify or sustain a verdict in her favor. James Dott*451ling was seventeen years and four months old, and the court instructed: “If you find that the plaintiff is entitled to recover, you would then give her what in your opinion would be the net amount that this young man would have earned during those three years and eight months until his arrival at the age of twenty-one years. You will determine, in the first instance, what would be the gross amount of his earnings for that period, and the evidence that has been submitted in that regard, viz: that he was earning $1.75 a day, is not conclusive on you, you might find that his earning capacity would increase or you might find that it would decrease; you will have to act as reasonable men in that regard and ascertain what in your opinion would be the reasonable amount he would earn in that period, taking into account his habits and health and ability to work and all the circumstances attending, and from that you will take the amount it would cost to maintain him, in the way of board, clothing, personal expenses and anything else that might occur to you as reasonable men that would be proper charges against it,, and the difference between the gross earnings and a reasonable amount deducted for the items just mentioned would be the amount you would return as your verdict on that feature of the case”; and in answer to a point the court said: “Where the parents sue to recover damages for the death of a minor child, as in this case, the measure of damages is the gross value in money of the child’s services from the date of death until it would have become 21 years of age, less the cost of its board, clothing and personal expenses, during said time.” The jury had before them the. fact that the plaintiff kept a boarding house, and the son lived at home with his mother and gave her all his earnings; they also had an opportunity of observing the plaintiff when upon the stand, and sufficient details to enable them to judge as to her and the injured lad’s position in life (Groves v. McNeil, 226 Pa. 345, 348); but there was no attempt to produce exact evidence con*452cerning the precise cost of maintaining tbe son during the balance of bis minority. It is not necessary to discuss tbe effect of a failure to produce such proof under ordinary circumstances, for at trial tbe defendants apparently were satisfied with tbe sufficiency of tbe proofs upon the point under discussion; when tbe plaintiff endeavored to bring forth further testimony upon this general branch of tbe case it was barred on tbe defendant’s objection, and later on they made no demurrer to tbe evidence as it stood, nor did they ask for any special instructions in relation thereto. This being tbe case, under tbe circumstances at bar, it is now too late to complain (Groves v. McNeil, supra, p. 348); Tbe instructions on tbe measure of damages were substantially correct, and it is apparent, particularly so far as tbe amount of the verdict is concerned, that tbe trial court took every care to guard tbe rights of tbe defendants; we are not convinced of material error.

Tbe assignments are overruled and tbe judgment is affirmed.