A person who is completely color-blind. There are two types. The rod monochromat appears to have totally defective cones: he has very poor visual acuity as well as the inability to discriminate colors. The cone monochromat has normal visual acuity: his cones appear to respond normally to light but to be completely unable to discriminate colors. It is possible in this case that the defect does not lie in the cones themselves but in the integration of the nerve impulses as they pass from the cones to the brain. Both types of color blindness are probably inherited.