§ 1. As distinguished from Physiological Reflex.— "We may define a reflex act," says Dr. Waller, "as the immediate motor response to centripetal excitation."* The emphasis here is on the immediacy of the response. The reaction depends directly on the stimulus, so that it always occurs in an invariable and inevitable manner whenever the stimulus is repeated, and is discontinued when the stimulus ceases to operate. If we irritate with acetic acid the thigh of a frog whose cerebral hemispheres have been removed, the leg is jerked away. By using a suitable apparatus it may be arranged that whenever the log is thus jerked away it comes in contact with a hot plate; when this happens, it is jerked back again. On being again irritated, it is once more jerked away and once more comes in contact with the hot plate, when it is again withdrawn; and so the process may go on until the limits of fatigue are reached.

A reflex act may be performed without being accompanied by change in consciousness, or at least by any conspicuous change. Coughing and sneezing are reflex acts, due to irritation of the mucous membrane. But a person may sneeze or cough either unconsciously or consciously.

* Human Physiology, p. 294. 125

Perhaps the unconsciousness is in any case not complete; but it is often very nearly so. The consciousness on the other hand is sometimes very keen, as when the irritation of the mucous membrane is violent. Now those reflex actions which, roughly speaking, take place unconsciously, may be described as physiological; those which take place with consciousness may be described as sensational. There is no reason for believing that the physiological reflex is effected through nervefibres other than those which convey and effect the sensation-reflex.

The sensation-reflex is the most primitive form of mental life which is distinctly recognisable. If, then, we fix the conditions under which the physiological passes into the sensational reflex, we thereby fix the conditions under which mental life first appears in a definite form. These conditions appear to be twofold. In the first place, the merely physiological reflex is found where the action takes place regularly and uniformly in response to stimulation which is uniformly and regularly recurrent. The sensation-reflex, on the other hand, takes place on a comparatively special emergency, which is only of occasional occurrence. In the second place, much depends on the degree in which the mind is preoccupied by higher processes. A man may cough unconsciously when he is absorbed in some interesting topic, although in a less preoccupied condition of mind the cough would have been a sensation-reflex. The more preoccupied he is, the more intense must the irritation be in order to produce an appreciable sensation. Taking up the first point, it is plain that those reflex movements which belong to the ordinary and normal routine of the vegetative life of the organism are almost wholly physiological. The heart's beat and its modifications, the constriction and dilatation of the bloodvessels, breathing, swallowing, the secretion of saliva, and the like, are not normally accompanied by distinctly appreciable sensations. I say distinctly appreciable sensations, because, in all probability, they do in their totality contribute to determine the state of consciousness as a whole, giving it a certain tone or modality. But the effects of the various organic processes blend into a vague total experience. Their several effects are not separately appreciable. The most we can say is that, as Dr. Michael Foster puts it, "if the whole of our abdominal viscera were removed, we should be aware of the loss as a change in our common or general sensibility."* On the other hand, when a stimulus is of comparatively occasional occurrence, and prompts a special combination of movements to meet a special emergency, the concomitant experience may disengage itself from the vague mass of general sentience and become salient in consciousness. The more special the occasion, and the more intense the stimulation, the more definitely does the sensation-reflex stand out in its own proper character as distinguished from the physiological reflex. Coughing is an act required only now and then, when irritating matter happens to be lodged in the throat. Hence in waking life it is usually a sensation-reflex, when the mind is not otherwise too much preoccupied, or when the irritation is intense enough to counteract even a strong preoccupation. The act of swallowing belongs to the fixed routine of vegetative life, and is not in the ordinary course of things accompanied by a separately appreciable experience. But if we touch the back of the tongue with a finger, or tickle it with a feather, this is an interruption of routine requiring a special adjustment adapted to the special emergency, which cannot be made without a wellmarked modification of consciousness. So, breathing is normally unconscious;* but if any difficulty or obstruction occurs in the respiratory process, it at once becomes accompanied and prompted by painful sensations.

* TextBook of Physiology, book iii., ch. vi., p. 1421.

On the second point we need not say much. Where the mind is much preoccupied, we may have a physiological reflex where otherwise we should have had a sensational reflex. As an extreme example of the effect of mental preoccupation we may refer to the soldier who in the heat of the battle is unaware of being wounded. What most concerns us is the fact that at the lower levels of organic life, where action is largely or mainly reflex, so that higher processes play a comparatively small part, there can be very little mental preoccupation. Thus, the lower we descend in the scale, the stronger is the presumption that a reflex act adapted to meet an occasional emergency is of a sensational and not merely of a phsysiological character.

* This means that the breathing-sensations are normally merged in the mass of general sentience; they are not normally prominent in consciousness, as they are when breathing is obstructed.