We call general sensations those feelings, pleasurable or otherwise, which can be excited without our being able to refer them to external objects, compare their sensation with those of the special senses, or even describe their exact mode of perception. Under this head are enumerated Pain, Hunger, Thirst, Nausea, Giddiness, Shivering, Titillation, Fatigue, etc.

Of these only pain is commonly referred to any given part, and the attempt to localize pain with exactness soon shows how very different is our power in this respect, in the case of pain and in the case of tactile impressions. Thus, when we strike our "funny bone" (the ulnar nerve passing over the condyle of the humerus), by the tactile impressions of the skin we know the elbow is the injured part, but the locality of the pain is not so exactly to be determined, for it shoots down the arm to the little finger, and is indefinitely spread over the region to which the nerve is distributed.

In studying the laws which govern the perception of painful impressions, we must make the experiments upon ourselves, since we alone can form conclusions from the sensations produced.

The best way to carry out experiments upon pain is to use extremes of temperature, as we can thus graduate the stimulation. The application of a liquid over 500 C., or below 20 C., causes pain. The suddenness of application to the part, and its duration, and the extent of surface, as well as the previous temperature, have important influence in the amount of pain produced.

The various kinds of pain with which we are all more or less familiar seem to be related in some way to their mode of production, but we are unable to assign any definite cause for these differences of character. Thus, though such terms as shooting, stabbing, burning, throbbing, boring, racking, dragging pain, are frequently used, and may be of diagnostic value, we have only an indistinct knowledge that throbbing depends on excessive vascular distention in a part, that sharp pains are produced by sudden excitation of a sensitive part, and the dull pains by the more permanent stimulation of a part less well supplied with nerves.

Further, pain, as we think of it, is a complex mental process, made up of many items, such as real sensory impressions, fear, disgust, etc. When a finger is to be lanced, patients often cry out most loudly before they are touched with the knife, and show intense feeling when they look at the blood flowing from the wound.

Hunger and thirst are peculiar and indefinite sensations which are experienced when some time has elapsed since food or drink has been taken. The exact part of the nervous system in which these impressions arise has not been determined. They are, however, said to be associated with peculiar sensations in the stomach and throat respectively. In the same way the venereal appetite, though associated with local sensations, cannot be referred to any one part of the nervous system.

Nausea is also a sensation which cannot be attributed to any part of the nervous centres. It commonly arises in response to afferent impulses, such as smells, sights, tastes, pharyngeal, gastric or other visceral irritation, and is antagonistic to the appetites just named. All the sensations that give rise to or precede nausea are asssociated in our minds with disagreeable impressions, and no doubt mental operations have much to do with its production. A child, free from affection, may be heard to say of a castor-oil bottle which in itself is not ugly, " I can't bear to look at it; the very thought of it makes me feel sick.':

Without any participation on the part of the mental functions, unavoidable nausea may come on from irregular movement, as that of a ship, which often causes nausea in those unaccustomed to the sea. Certain conditions of the blood flowing through the nerve centres also causes nausea, as when emetics are injected into the blood.

Giddiness, which consists of a feeling of inability to keep the normal balance, is often produced in connection with the last by irregular movements, but more surely by a rotatory motion of the body. Other afferent influences may give rise to it, viz., from the stomach, in some cases of irritation; from the eye, when we look from a height; from the semicircular canals of the ear by rotation of the body; and also from conditions of the blood, as in alcoholic toxaemia.

Shivering is the result of a peculiar nervous effect produced by afferent influences of an unpleasant kind; the sudden application of cold to the skin, a revolting sight, a shrill noise, or an intensely nasty taste - all excite a nervous condition which makes us shiver.

Titillation follows light stimulation of certain parts of the cutaneous surfaces. It is a peculiar general sensation, in moderation not disagreeable, and usually accompanied by a tendency to meaningless laughter and other reflex movements.