CLASSIFICATION OF THE SENSE ORGANS 729 



3. Rapid vibrations in ether, or waves in immaterial media, received by the 

 temperature corpuscles of the skin (heat-rays) and the retinae of the eyes (light- 

 rays). These vibrations, however, also include some to which we are absolutely 

 insensitive or which can only be perceived with the help of certain accessory means. 

 The Hertzian electrical waves attain a vibratory frequency of 3000 billions per 

 second, the ultra-violet rays one of 5,100,000 billions per second, and the Roentgen- 

 rays one of 6,000,000,000 billions per second. In between these two extremes 

 lies the receptive scala of man. Thus, we find that our retina is capable of receiving 

 impacts, the vibrations of which vary between about 400,000 and 800,000 billions 

 per second. This range covers the solar spectrum. Between these vibrations and 

 those attaining a frequency of 3000 billions per second, lies the realm of the radiant 

 heat which stimulates the temperature receptors of our skin. 

 B. Chemical Energy. 



The different chemical impacts to which we may be exposed, are received in a 

 relatively imperfect manner. The organ of smell covers a much wider range than 

 the organ of taste; in fact, the latter gives rise to only four fundamental sensations, 

 namely, sweet, bitter, salty and sour. 



Classification of the Sense-organs. — The foregoing discussion 

 shows first of all that under ordinary conditions only a limited number 

 of the energies developed in space, are made accessible to man. This 

 statement, however, is not meant to imply that the equipment of other 

 animals is as good as that of man; in fact, the chances are that it is 

 not, for the reason that the human nervous system attains the most 

 perfect all around development. It cannot be doubted, however, that 

 the sensory mechanisms of a particular group of animals may be more 

 fully developed along certain lines than those of others. This is especi- 

 ally true of the olfactory apparatus ; but may also be true, for example, 

 of the visual and auditory mechanisms of the birds as against those 

 of man. At all events, provision has been made in each case to equip 

 the different animals more especially with those sense-organs which 

 are of greatest practical use to them. 



Man has been placed in a position to analyze the energy manifes- 

 tations in space by means of five senses, i.e., he is able to bring five 

 different means to bear upon the forces of nature for purposes of 

 orientation. The sense-organs concerned in this analysis, are com- 

 monly said to be the eyes, ears, nose, tongue and skin. In agreement 

 with this classification the layman recognizes five senses, namely, sight, 

 hearing, smell, taste and touch. One discrepancy, however, must 

 occur to us immediately, namely, that this classification does not em- 

 brace the large number of different receptors which are concerned with 

 the reception of stimuli arising in the interior of our body. In the 

 second place, attention should be called to the fact that several of the 

 original five senses are really composite in type. Obviously, the ear 

 contains not only the organ of hearing, but also separate receptors for 

 the static and dynamic senses. Quite similarly, the skin is not only 

 concerned with touch, but also mediates the sensations of pressure, 

 pain, and temperature. To be brief, it will be brought out later on 

 that there are in reality more than twenty different receptors in our 

 body.^ 



^Ohrwall, Skand. Archiv fiir Physiol., xi, 1901. 



