Influence of photic stimulation and hypothermia on the electromyogram of the developing chick

¹ Department of Biology, Xavier University, and Department of Anatomy, College of Medicine, University of Cincinnati, Cincinnati, Ohio

As the body temperature of developing chicks between the 18th day of incubation and the 3rd week after hatching was lowered from normal to 16 C, the eye was subjected to photic stimulation and electrical recordings were made from the eye, cerebral lobes, and shank muscles. As body temperature drops photic stimulation modifies the amplitude of muscle potentials by first producing reduction in amplitude (35–25 C), then brief augmentation (20–24 C), then prolonged augmentation (20–16 C), first, with the onset of photic stimulation and later with the cessation of photic stimulation. These effects are most pronounced in chicks between the 20th day of incubation and 1 week after hatching.