Abstract: A head positioner for radiologic and other medical procedures and a method for forming the head positioner are disclosed. A plastic rear component engages the backside of the patient's head, left and right plastic components engage each auditory meatus of the patient and a front component engages the nasion of the patient. Pressure is applied at the points of engagement and the components are secured to form a unitary headband structure. The headband is capable of repeated and periodic use in positioning the cranium of a human skull in precisely the same position relative to radiologic or other medical equipment. Apparatus for forming the headband structure is also disclosed.

Abstract: A notched tubular cutting instrument for use in vitrectomy is provided. An elongated tubular housing is formed with a cutting orifice in its tip. A resilient, inner tubular blade reciprocates within the housing. The housing is bent to bias the blade against the edges of the cutting orifice. The cutting orifice is a notch in the tubular housing having a cutting edge and two side edges. The cutting edge has a rake of more than 10.degree.. The side edges and cutting edge continuously guide the blade across the orifice and provide a shearing action between the blade and the cutting edge.

Abstract: A proportioning system is provided for mixing dialysate used in an artificial kidney machine. A first conduit carries concentrate solution in a recirculating loop pattern. A second conduit carrying water intersects the first conduit. At the point of intersection, the first conduit has an orifice for discharging concentrate into the flowing water. Concentrate is supplied to the first conduit through a supply line immersed in a storage jug. The supply line has a pressure-operated check valve through which concentrate passes only when required.

Abstract: A cutting instrument is provided, particularly applicable to vitreous surgery, having an elongated, tubular housing formed with a cutting orifice near its end. A resilient, inner tubular member is slidably mounted coaxially within the tubular housing. The tubular housing is bent in a manner to displace the cutting orifice in a direction toward the resilient, inner tubular member. As the end of the resilient, inner tubular member passes across the cutting orifice, it is resiliently urged into shearing contact with the cutting orifice.