What is the burden of proving that the appellant was negligent and that negligence was the proximate cause of the explosion?

Of course the burden of proving that the appellant was negligent and that its negligence was the proximate cause of the appellee's injury was on the appellee. That burden, however, was sustained prima facie by the evidence tending to show the explosion was caused by a failure to guard against a blowing of the valve by securely tightening the packing nut. The installation had been undertaken by the appellant and it was reasonable for the jury to find that it had been negligently performed. If so, it was certainly permissible for the jury to find also that such negligence was the proximate cause of the appellee's injury. Consequently, we cannot hold as a matter of law that the conclusions reached from these reasonable inferences were mere speculation and conjecture. Lavender v. Kurn, 327 U.S. 645, 66 S.Ct. 740, 90 L.Ed. 916; Tenant v. Peoria & Pekin Union Ry., 321 U.S. 29, 64 S.Ct. 409, 88 L.Ed. 520.