734 



SPECIAL SOMATIC AND VISCERAL RECEPTORS 



log Rj in which S indicates the sensation, R the stimulus and C the 

 constant represented by the difference in the sensation. But this 

 conception, that the sensation is proportional to the logarithm of 

 the stimulus, must meet with serious objections, because it has been 

 proved that Weber's law is not applicable to stimuli of low and high 

 intensity. In addition, Fechner has assumed that the smallest 

 appreciable increase in the sensation must always remain the same, 

 i.e. J the difference in the sensation obtained when 1 gram is added to 30 

 grams, must be the same as that evoked by the addition of 2 grams 

 to 60 grams. Physiological observation has proved this assumption to 

 be incorrect, and hence, we may justly advocate the view of James, 

 that the attempt to measure sensations with mathematical precision, 

 is a mere speculation. 



CHAPTER LX 



THE SENSES OF PRESSURE OR TOUCH, PAIN, AND 

 TEMPERATURE 



The Structure of Cutaneous Receptors, — The integument of our 

 body is permeated by two sets of nerve-plexuses, one of which is situ- 

 ated in the panniculus adiposus and the other 

 in the stratum subpapillare. Both ramifi- 

 cations give rise to fibrils which terminate 

 in peculiar end-organs in almost all layers 

 of the skin. The most common of these 

 consist of meduUated fibers from the dermal 

 plexus which give off branches and soon lose 

 their medullary sheath. The latter pierce 

 the epidermis and then form arborizations 

 among the cells of the Malpighian layer. 

 The different fibers end bluntly or are ex- 

 panded into distinct sensory plates. Phylo- 

 genetically considered the latter formation is 

 the more recent. 



The corpuscles of Meissner (1852) are found m 



* '^ the papillary and subpapillary layers of the skin. 



FiQ. 3 61. — Tactile Cor- They acquire a length of from 40-lOOjU and exhibit 



puscLE WITHIN A Papilla OF au oval OF Tound-elUptical outline. Their outer zone 



THE Skin OF THE Hand. Stained consists of connective tissue lamella which invest a 



WITH Chlobid OF Gold. {Ran- ^^^^ ^^ reticular tissue through which one, two, or 



several non-medullated nerve fibers wind their way 

 n Two nerve-fibers passing spirally to the tip of this structure. A very similar 

 arrangement is presented by the Golgi-Mazzoni cor- 

 puscle (1880) as well as by that described by Vater 

 and Paccini (1840). The latter are small oval 

 bodies which attain a length of from 2-4.5 mm. and a breadth of 1-2 mm. Their 

 outer zone consists of concentric lamellae, while their core is penetrated by a nerve 



to the corpuscle; a, a, varicose 

 ramifications of the axis-cylin- 

 ders within the corpuscle. 



