conditions. A fuller discussion of the circumstances
of this connection will be attempted hereafter. But,
in the meantime, it must be borne in mind that this
reference to nervous activity as preceding sensation is no
explanation whatever of sensation in itself, but simply of
the physical conditions upon which sensation is felt
in consciousness. A sensation can be known only
in consciousness, and as sensations are the simplest
mental facts which consciousness affords, we cannot✔
resolve them into any simpler elements, although
it is possible that some complex sensations may be
reducible to simpler ones. Our analysis of sensation
will therefore be completed when we have (1)
arranged them into clearly-defined classes (2)
resolved complex sensations into their simpler
elements as far as can be done, and (3) determined
how far this resolution can be effected, and especially
if conscious sensations can be legitimately analysed
into elements of which we are not conscious.

§ 15. Everyone is familiar with the five senses, or gateways of knowledge, as they have been called, by which we know the qualities of the external world. But, in addition to the sensations connected with these senses, it has been found necessary to form another class comprehending a variety of sensations clearly distinguished from the former. This class comprises all the sensations connected with the different parts of the organism with the exception of the five senses. This class and the sensations comprehended in it have been denominated variously, the vital sense, the organic sense, the sensations of

CHAP. II.

SECT. II.

Classification of sensations.

CHAP. II.

SECT. II.

organic life, &c. A clear view of the great variety of sensations of which we are conscious may be obtained by the study of the following table :

I. From a glance at the parts of the organism referred to in this class, it will be readily apparent what sensations are indicated. The organs concerned in muscular exertion give rise to different sensations when in a state of repose, when active, when fatigued, and when resting after labour. The nervous system may suffer excitement or depression in various degrees or manners, and give rise to a variety of sensations. Hunger, thirst and their opposites, with the sensations connected with them, depend upon certain states of nutrition and circulation. From a general condition of the body, which cannot be very clearly defined, there arise feelings of languor or the opposite, and also heat and cold; the sensations of the latter kind being, however, chiefly felt in the skin. The respiratory system is the seat of a class of sensations such as that of suffocation, and there are sensations also connected

with the digestive organs. The general characteristics of these sensations are that they arise in the organism itself as the concomitants of vital operations, and that they are accompaniments, results, or stimulants of action, not elements of knowledge.

II. The sensations of intellectual life are those whose chief end appears to be the imparting of knowledge regarding external things.

Two of these senses are so closely connected with the respiratory and digestive systems, and give us comparatively so little extra organic knowledge, that their sensations occupy a middle position between those of the first class and those of the more intellectual sense which we have placed last in order. The sense of smell, placed at the portal of the respiratory organs, gives notice of the entrance of any noxious vapour into the lungs, and occasions the sensation of smell when any odorous emanations come into contact with the olfactory nerves. "The sense of taste is that by which we distinguish the sapid properties of bodies. The term, as commonly understood, includes much more than this; being usually employed to designate the whole of that knowledge of the qualities of a body (except such as is purely tactile) which we derive through the sensory apparatus situated within the mouth. But this is dependent upon the assistance of the olfactive sense, which is affected by the odorous emanations of all such bodies as are capable of giving them off; and the indications of which are so combined with those of the true questative sense as to

CHAP. II.

SECT. II.

Senses of

smell and

taste.

CHAP. II.
SECT. II.

make an apparently single impression upon the sensorium. Moreover, there are certain sensorial impressions received through the organ of taste, which are so nearly allied in their character to those of touch, as to render it difficult to specify any fundamental difference between them; such are the pungent sensations produced by mustard, pepper, the essential oils, &c., all of which substances, when applied for a sufficient length of time to any part of the cutaneous surface, produce a sensation which can scarcely be distinguished from that excited through the organs of taste, in any other way than by its inferior intensity, and by the absence of the concurrent odorous emanations. The taste of such substances might, therefore, perhaps be considered as the composite result of the impressions made upon the sensorium through a refined and acute touch, and by the effect of their odorous emanations upon the organ of smell."*

The sensations both of smell and taste may be arranged in a loose popular way into subordinate classes; such as pungent, acrid, sweet, &c. But as no classification having any pretence to scientific accuracy and exhaustiveness has yet been offered, the subject does not demand much of our attention. It may be remarked by the way that there are certain well-defined classes, inasmuch as the sensations of one class, such as the bitter, cannot, by any means of which we are aware, be transformed into those of another. II. We now come to the study of the sensations of * Carpenter, 'Human Physiology,' p. 177.

CHAP. II.

SECT. II.

Original distinguished from acquired knowledge in sensa

the more intellectual of the special senses-touch,
hearing, and sight. And it will be necessary to
distinguish carefully between those which are pro-
per and original to those senses and those which are
acquired. We have seen already that in the case of
two of these senses, hearing and sight, the sensation
undergoes a process of objectification, being referred tion.
to a distance. In the case of touch this is not so
obvious, although it is still true to a certain extent.
The sensation of pressure, which is in itself purely
organic, is referred to something not at any distance,
it is true, but still external to the organism. Now,
in each of these cases the objectification of the
sensation, not being original, must be distinguished
from the sensation itself.

touch.

The sense of Touch has, as its proper organ, the Sense of skin, which "is peculiarly adapted for this purpose, not merely by the large amount of sensory nervous fibres which are distributed in its substance, but also by its possession of a papillary apparatus in which these nerves for the most part terminate, or rather commence.' The tactual sensation proper is that which is felt when any body slightly comes into contact with the skin so as to make its presence felt. But this tactual sensation is often combined and confounded with others of a different kind. When, for example, the point of the finger is pressed against the table, in addition to the tactual sensation, there is a feeling of resistance or hardness which is manifestly the sensation of muscular exertion objectified. Where the finger is rubbed over the surface of