Manufacturer was not indicated.  This is a heated pneumotach with is indicated by the black knob on the side which is actually the screw-on cover for an electrical post.   From Medical Instrumentation for Healthcare, by Cromwell L, Arditti M, Weibell FJ, Pfeiffer EA, Steele B, Labok J.  Published by Prentice-Hall, 1976.  Page 267.