Dollken has put forward a theory based on the condition of the blood and the state of the nerve elements. According to him arbitrary reduction of the activity of the sense-organs accompanied by reduction of the associative activity to a minimum produces anaemia of the brain. The cortex and cortical paths participate in this process, but what share the subcortical elements have in it, has yet to be shown. According to Dollken a certain tonicity of the nerve-elements results from this anaemia, rendering them responsive to stimuli far below the normal limit in strength. The nerve-elements are thus enabled individually to acquire a better state of nutrition and the increase of functional capacity arising therefrom. Still this particular tonicity might also be considered primary.

Failure to distinguish clearly between cause and effect is one of the sources of error frequently found in those theories of hypnosis which are based on the state of the circulation of the blood in the brain. Even when there is a change of circulation in the brain in hypnosis, it is a mistake to think that the changed circulation causes the changed functions. Haas very properly points out that when a person who feels ashamed blushes, it is not the blushing that causes the feelings of shame. As a muscle needs more blood when it is at work, but does not work more because more blood flows to it; as the stomach when digesting needs more blood than when it is inactive, it is also not improbable that the brain, or portions of it, when they are active need much blood, and when they are inactive but little. Then if we take the vasomotor disturbances as proved, it is by no means proved whether they are the cause or the effect of hypnosis.

In fact, Cappie takes the opposite view. He thinks that the increased activity of the motor centres in hypnosis draws too much blood to them, thereby causing anaemia of the other portions of the brain which are necessary to consciousness. But this theory does not give a satisfactory explanation, for it arbitrarily opposes the motor centres to the parts of the brain necessary to consciousness, and there is always consciousness in hypnosis. The principle from which Cappie starts is the one put forward by Brown-Sequard. He thinks that hypnotism is the sum of dynamo-genetic and inhibitory acts - i.e.., that the increased action of certain parts of the brain (dynamogenetic act) causes decreased action of others (inhibitory act). That Fechner recognized these principles very clearly is shown by the fact that he spoke of the antagonism existing between the various spheres of psychophysical activity. He was also fully aware of the important parts played by nutrition and the circulation of the blood.

The theory of an antagonistic distribution of the blood was used later on by Meynert to explain morbid mental states.

Just as Cappie assumed that there is during hypnosis an altered activity of certain centres and associated changes in the circulation, so Wundt has suggested as the physiological basis of the phenomena of hypnosis a double interaction, neurodynamic and vasomotor. The irritability of any central element depends not only on its own condition at the moment of stimulation, but also on the condition of the other elements with which it is in association, in such a way that excitation of the neighbouring element lowers its own excitability, while a condition of inhibition favours discharge of energy. This is the neurodynamic reaction. At the same time, according to Wundt, there is a vasomotor reaction, for the blood contents and functions of the organs stand in such a relationship to one another that increase of function produces increased flow of blood, decrease of function, depression of the blood flow. Wundt further argues that neurodynamic compensation favours vasomotor compensation and vice versst, and seeks in this way to explain the phenomena of hypnosis by viewing the chief symptoms from this standpoint. He then refers to the centre for apperception, which, hypothetically, he regards as the substratum of the process of apperception.

He believes that we have here an essential difference between dreaming and hypnosis, though he does not ascribe absolute importance to this difference. Certain phenomena of inhibition of the processes of the will and the attention are common to both, also a tendency to increased excitability of the sensory centres leading to hallucinatory interpretation of sense-impressions. But there are distinguishing characteristics; attention is only partially altered by suggestion in hypnosis, but the inhibition of the will in sleep affects both apperceptive and motor processes. It is from this psychological difference that Wundt develops his physiological theory. In dreams those central regions which are associated with the process of apperception are more or less in a state of inhibition, and nearly all the compensatory excitation is conducted to the sensory centres, but under certain circumstances in hypnosis a compensatory increase of irritability arises in the apperception-centre in opposition to the existing partial inhibition.

As I have already mentioned, Wundt has raised against my attempts at a psychological explanation, the objection that I have not answered the question why in hypnosis consciousness is not contracted. I have, however, put the questions which must be met by physiological answers (p. 268). The third question I put is this: What is the causal connection between this state and the methods which induce hypnosis and put an end to it? I do not find that this question is in any way answered by Wundt's physiological theory, and against Wundt's physiological explanation I must raise the same objection as he has raised against my psychological speculations. In addition to this, the centre of apperception as supposed by Wundt, is little more than a hypothetical assumption.

Vogt's theory is based on similar principles to Wundt's, but it contains a series of comprehensive and elucidatory ideas, especially that which he terms "constellation." By this Vogt understands the whole cerebral mechanism corresponding to a mental process, and he considers it the resultant of conscious and unconscious processes. He thinks that hypnosis is brought about by an alteration of this constellation, and he refers the phenomena of suggestion partly to inhibition, partly to increased irritability, and partly to the opening up of fresh paths. "Let us, for example, consider the mechanism of catalepsy. I lift up a hypnotized subject's arm. This passive movement causes a sensation of movement. The associative paths leading from the centre in which this idea of movement is localized are rendered non-conductors by the dissociative effect of hypnosis. In consequence of this the nerve-wave (neurokym) caused by the passive movement of the arm is, for the most part, transferred to the centripetal paths leading from the centre in which the idea of the movement was aroused, and thus sets up muscular contraction corresponding to the position passively imposed on the arm." Vogt also endeavours to explain other phenomena by the action of the neurokym (nerve-wave) - i.e., by the nervous excitation that reaches the cerebral cortex.