at the time by sensory cells.

Much more cannot be said

except as guess work. The physiological basis of an image is perhaps action similar to that in the corresponding percept but weaker, or (and to the author's mind far more probably) the action of only a portion of the cells. involved in the corresponding percept, the cells associated in the action being different in the two cases. In actual perception the brain action giving, say, the mere sight of the thing would be accompanied by brain action corresponding to the thing being in a certain place, being touched as well as seen, being felt as possessed of tendencies to be or do this or that. The neural correlate of a percept, say of a dog, would thus be a complex total. The mental image of the dog might well have as its neural correlate a weakened revival and of only a part of this total.

Still more hypothetical are all notions about the neural correlates of feelings of the third intention.

Of General Notions.-The physiological basis of a general notion is perhaps the neural correlate of some percept or image or sensation, commonly of a word, plus the half-aroused activities of the numerous associated sets of cells, each set of which would, if fully active, give the feeling of one of the particular things included in the class meant by the word. For instance, the concept 'a dog' would have as its physiological basis the cell action going with the image of the word 'dog' plus the halfaroused action of the cells which if fully active would give images of different particular dogs.

Of Individual Notions.-The physiological basis of an individual notion is probably the neural correlate of some percept or image or sensation, commonly of a word, plus action in other cells which would, if allowed to dis

charge on into their associated cells, lead to the image or percept of the thing or person referred to by the individual notion. Thus the thought of 'Napoleon' may have as its physiological basis the cell action going with the word 'Napoleon' plus the half-aroused action of the cells which if fully active would give images of Napoleon or of his various acts and characteristics.

Of Feelings of Relationships.-Feelings of logical relationships may have as their basis the states of transition in the brain from the activity of one set of neurones to that of others. For instance, the feeling of unlikeness may have as its parallel the simultaneous waning of one. brain process and the waxing of one different. Some feelings of relationship may be semi-emotional feelings, and due to the same type of neural action as parallel emotions. Thus the feeling of the relation of cause and effect may be a feeling of justified expectancy.

Other hypotheses about the neural basis of mental states are that the greater or less intensity of a mental state is due to a greater or less violence of the conducted stimulus; that the personal feeling which characterizes mental states is related to the constantly acting cells stimulated by ever present bodily conditions; that the broad qualities of mental life which we call temperament or disposition are related to cell action due to the condition of the blood. About the physiological activities which go with feelings of time, belief, desire, choice and many other types of feelings, so little is known or even guessed that it is unwise to note the speculations about them.

Of Mental Connections.-The physiological basis of the connections between ideas, acts, and ideas and acts is much clearer than the physiological basis of the varieties

of ideas. These connections are throughout based on the connections between neurone and neurone in the nervous system, the existence of paths of easy conduction for the nervous stimulus.

Reflexes and instincts are the manifestations in conduct of connections between neurones due to the natural organization of the human body. Acquired habits of thought and conduct represent the connections between neurones by which the nervous system has adapted itself to the individual's needs. When in Part III the growth of mental life and the laws of its action are described, the dependence of the connections between the parts of a human life of thought and action upon the connections between parts of the nervous system will be seen everywhere to be a natural, almost the inevitable, conclusion.

Exercises

Experience 13. The Influence of the Absence of Neurone Endings in a Portion of a Sensitive Surface.—The neurones composing the optic nerve form a compact bundle of fibres where they enter the retina. Where this bundle enters there are no rods or cones or bi-polar neurones, nothing in fact to be stimulated by light.

Close or cover the left eye. Look with the right eye steadily at the cross in Fig. 62. When the book is about seven inches from

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FIG. 62.

It is essential that the The reason for the nondistance the image of where the optic nerve

the eye the circle will not be seen at all. eye be kept fixed steadily on the cross. appearance of the circle is that at that the circle on the retina falls on the spot enters. Move the book slowly to a greater distance, fixating the cross as before. Soon the circle will reappear and the square dis

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appear. Why? How may the figure be used to demonstrate the existence of the similar 'blind spot' in the left eye?

From this experiment it would appear that every field of view seen by a single eye should have an unseen spot or patch.

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FIG. 66.

Perform a similar experiment with Figs. 63, 64, 65, 66 and 67. When the circle falls on the blind spot, what takes its place in each case? State the rule which seems to hold concerning what happens in the case of vision in the absence of neurone endings in a portion of a sensory surface.

Sensations from Bilaterally Symmetrical Sensitive Surfaces. Experiment 14.-If you touch the desk simultaneously with the right and left forefingers, you feel two touches, but if you