Bergson then examines the physiological aspects of the perceptual process. Beginning with reflex actions and the development of the nervous system, he goes on to discuss the functions of the spinal cord and the brain. He finds in regard to these last two that "there is only a difference of degree--there can be no difference in kind--between what is called the perceptive faculty of the brain and the reflex functions of the spinal cord. The cord transforms into movements the stimulation received, the brain prolongs into reactions which are merely nascent, but in the one case as in the other, the function of the nerve substance is to conduct, to co-ordinate, or to inhibit movements.[Footnote: Matter and Memory, pp. 10-11 (Fr. p. 9).] As we rise in the organic series we find a division of physiological labour. Nerve cells appear, are diversified and tend to group themselves into a system; at the same time the animal reacts by more varied movements to external stimulation. But even when the stimulation received is not at once prolonged into movement, it appears merely to await its occasion; and the same impression which makes the organism aware of changes in the environment, determines it or prepares it to adapt itself to them. No doubt there is in the higher vertebrates a radical distinction between pure automatism, of which the seat is mainly in the spinal cord, and voluntary activity which requires the intervention of the brain. It might be imagined that the impression received, instead of expanding into more movements spiritualizes itself into consciousness. But as soon as we compare the structure of the spinal cord with that of the brain, we are bound to infer that there is merely a difference of complication, and not a difference in kind, between the functions of the brain and the reflex activity of the medullary system." [Footnote: Matter and Memory, pp. 17-18 (Fr. p. 15).] The brain is no more than a kind of central telephone exchange, its office is to allow communication or to delay it. It adds nothing to what it receives, it is simply a centre where perceptions get into touch with motor mechanisms. Sometimes the function of the brain is to conduct the movement received to a chosen organ of reaction, while at other times it opens to the movement the totality of the motor tracks. The brain appears as an instrument of analysis in regard to movements received by it, but an instrument of selection in regard to the movements executed. In either case, its office is limited to the transmission and division of movements. In the lower organisms, stimulation takes the form of immediate contact. For example, a jelly-fish feels a danger when anything touches it, and reacts immediately. The more immediate the reaction has to be, the more it resembles simple contact. Higher up the scale, sight and hearing enable the individual to enter into relation with a greater number of objects and with objects at a distance. This gives rise to an amount of