The stimuli that thus pour in upon the individual, and to which he must react, must find an organism ready to respond in some way or other. A sleeping man naturally does not adjust himself to danger, nor does a paralyzed man fly. The most attractive female in the world causes no response in the very young male child and perhaps stirs only reminiscences in the aged. Food, which causes the saliva to flow in the mouth of the hungry, may disgust the full. Throughout life there are factors in the internal life of the organism instantly changing one's reaction to things of physical, mental and moral significance. He talks loudest of restraint and control who has no desire; and in satiation even the sinner sees the beauty of asceticism. There must be a coincidence of stimulus, readiness and opportunity for the full, successful response to take place.[1] [1] A slang epigram puts it better: The time, the place, and the girl. The simplest response to any stimulus from the outer world is the reflex act. Theoretically a reflex act is dependent upon the interaction of a sensory surface, a sensory nerve cell, a motor nerve cell and a muscle, i. e., a receptive apparatus and a motor apparatus in such close union that the will and intelligence play no part. Thus if one puts his finger on a hot stove he withdraws it immediately, and such responses are present even in the decapitated frog and human for a short time. So if light streams in on the wide-open pupil of the eye, it contracts, grows smaller, without any effort of the will, and in fact entirely without the consciousness of the individual. Swallowing is a series of reflexes in a row, so that food in the back part of the mouth sets a reflex going that carries it beyond the epiglottis; another reflex carries it to the esophagus and then one reflex after the other transports the food the rest of the way. Except for the first effort of swallowing, the rest is entirely involuntary and even unconscious. Those readers who are interested would do well to read the work of Pavlow on the conditioned reflex, in which the great Russian physiologist builds up all action on a basis of a modification of the primitive reflex which he calls the "conditioned reflex."[1] [1] Pavlow is one of the scientists who regard all mental life as built up out of reflexes. The immediate reflex is only one variety; thought, emotion, etc., are merely reflexes placed end to end. Pavlow divides action into two trends, one due to an unconditioned reflex, of innate structure, and the other a modified or conditioned reflex which arises because some stimulus has become associated with the reflex act. Thus saliva dripping from a dog's mouth at the smell of food is an unconditioned reflex; if a bell is heard at the same time the food is smelled then in the course of time the saliva flows at the sound of the bell alone,--a conditioned reflex. A very complex system has been built up of this kind of facts, which I have criticized elsewhere.