Possibilities are like the wings of birds; they allow man to soar and to climb to the heavens. And facts are like the atmosphere against which those wings must beat, and without which the soaring bird will surely plummet back to earth.

Do not become archivists of facts. Try to penetrate to the secret of their occurrence, persistently search for the laws which govern them.

But man has still another powerful resource: natural science with its strictly objective methods.

As was to be expected, the discovery of the nervous apparatus of the salivary glands immediately impelled physiologists to seek a similar apparatus in other glands lying deeper in the digestive canal.

One can truly say that the irresistible progress of natural science since the time of Galileo has made its first halt before the study of the higher parts of the brain, the organ of the most complicated relations of the animal to the external world. And it seems, and not without reason, that now is the really critical moment for natural science; for the brain, in its highest complexity-the human brain-which created and creates natural science, itself becomes the object of this science.

When the dog is repeatedly teased with the sight of objects inducing salivary secretion from a distance, the reaction of the salivary glands grows weaker and weaker and finally drops to zero.

In the dog two conditions were found to produce pathological disturbances by functional interference, namely, an unusually acute clashing of the excitatory and inhibitory processes, and the influence of strong and extraordinary stimuli. In man precisely similar conditions constitute the usual causes of nervous and psychic disturbances. Different conditions productive of extreme excitation, such as intense grief or bitter insults, often lead, when the natural reactions are inhibited by the necessary restraint, to profound and prolonged loss of balance in nervous and psychic activity.