234 'Journal of Comparative Neurology and Psychology. 



anomalies are not sufficiently discussed. A full account of tliis recent work, 

 witli criticisms of special parts of it, will be found in a forthcoming number 

 of the Journal of Philosophy, Psychology and Scientific Methods. In this 

 review I shall make a careful comparison of the present work with that of 

 Rivers and Head, and with that of Trotter and Davies {Journal of Physiology, 

 London, 1909, vol. 38, pp. 134-246), which has also appeared since my articles 

 have been in type. At present I wish to call attention to only a few matters 

 reported in these two recent articles. 



The recovery of sensibility to light touch is considered by Rivers and 

 Head to be dependent upon the regeneration of the so-called touch spots. 

 These touch spots are, according to these authors, grouped about the hairs 

 and much, if not all, of the sensibility of the hairs depends upon the presence 

 of the nerve endings which make up these touch spots. They say, for example, 

 "Over hair-clad parts these touch spots are strictly associated with the roots 

 of the hairs, they express the sensibility to mechanical stimuli to that part 

 of the hair which lies beneath the surface of the skin. Almost every hair is 

 a delicate tactile sense-organ ; any movement of its tip is transmitted to its 

 root with the increasing power of a lever, setting up tactile impulses." We 

 find, however, they report in one part of their paper that tactile sensations 

 (sensations to light touch) could be evoked only after a period of 365 days 

 following the operation, but in another place we are informed that "No sen- 

 sations were obtained from the hairs until 86 days after the operation, when 

 there were found four hairs that gave a sensation when they were plucked." 

 It is also noted that 161 days following the operation the hairs on the arm 

 were sensitive to the stimulation of brushing with cotton wool, although the 

 sensibility to light touch did not return for 365 days. Surface indications are 

 that Rivers and Head were dealing with the same form of dissociation of the 

 hair sensibility which has been described by me in the foregoing papers, but 

 that they did not carefully investigate this matter. At any rate, from their 

 account of the sensibility of the hairs we are justified in assuming that the 

 hair sensibility was found by them to be independent of the presence of dis- 

 tinct touch spots and that their observations upon the sensibility of the hairs, 

 casually reported, support the view expressed in the foregoing paper. 



According to Rivers and Head all temperature sensations also depend upon 

 sensation spots, and the difi'erences in temperature sensations described by 

 Head and Sherren in a former paper are now reported to be due to the 

 presence of a greater or less number of cold or hot spots in the epicritic 

 and protopathic areas respectively. Head still holds the view that in an 

 area in which there is no epicritic sensibility only the extremes of temperature 

 will be appreciated, while in the area endowed with epicritic sense there 

 is the ability to appreciate the intermediate degrees of temperature. It Is not 

 clear that Head had sensations similar to those of my subject, but we read 

 "It would seem that the number of spots stimulated is of greater Importance 

 than the intensity of cold by which the sensation is evoked." In experi- 

 ments in which his arm was tested by cold areas of different size Head reported 

 a cool large area to feel colder than an ice cold small area, in the former 

 case there being a number of spots stimulated and in the latter only one. 



