CHAPTEE I 



CUTANEOUS SENSIBILITY 



CONTENTS. 1. Difference between modality and quality of sensations. Johannes 

 Miiller's law of specific energies. 2. Different intensities of sensations. Weber's 

 law and Fechner's law. 3. Transformation of sensations into perceptions : 

 philosophical theories. 4. Four modalities of cutaneous sensation, according to 

 Blix, Goldscheider, and v. Frey. 5. Cutaneous nerve - endings for sensations of 

 pressure, pain, cold, and heat. 6. Physiological analysis of thermal sensations 

 (heat and cold). 7. Touch and pressure sensations. 8. Capacity for localising 

 cutaneous sensations. 9. Pain sensations. Bibliography. 



MOVEMENT and Sensation are the two extremes of the processes 

 of animal life by which the organism is brought into direct 

 relation with the outer world. Movements are always objective 

 in character and can be studied directly by external observation. 

 Sensations are invariably subjective, and can only be directly 

 analysed by introspection, and indirectly inferred from the 

 expressional movements which are their external concomitants. 

 It follows that the physiology of sensation in man is the necessary 

 starting-point for the comparative physiology of sensation in 

 animals ; and the intimate observation of our own consciousness 

 is the only available basis for judging the psychical activities of 

 animals or of other men. 



All organs of the body that are supplied with afferent nerves 

 continually send information of their functional state to the 

 central nervous system, and exert a reflex controlling influence 

 along the efferent nerves without passing the threshold of 

 consciousness. At other times they send to the centres messages 

 which are not entirely subconscious, but emerge vaguely and 

 indefinitely in consciousness as a more or less decided sense of 

 well-being or the reverse. Or again, the messages from the 

 different organs to the centres may definitely cross the threshold, 

 of consciousness and give rise to distinct sensations which differ 

 in quality and intensity. 



The complete excitation or functional activity of a sense is 

 always a psycho -physical phenomenon that is a physiological 



VOL. IV 1 B 



