38 



NA TURE 



[March i i, 1909 



once from M. D;iiine's results that the period of radio- 

 uranium must be long compared with that of uranium X. 

 Thus M. Danne's discovery neither assists nor makes it 

 more difficult to explain the results recorded in this letter. 

 It is obvious that we have here really a very complex series 

 of changes not capable of immediate interpretation. 



Frederick Soddy. 



Are the Senses ever Vicarious? 



It is a prevalent opinion that if a human being is bereft 

 of one sense, one or more of the other senses become more 

 acute, and thus establish a compensation. For example, 

 it is generally believed that the blind have the senses of 

 touch and of hearing, more especially of touch, developed to 

 a degree of acutcness not found in those who see, and 

 that, in this way, the blind find their way about the world 

 with an accuracy that is often surprising. The blind 

 have even been credited with the ability to discriminate 

 colours by the sense of touch, and some have attempted 

 to support this supposition by an appeal to the sense of 

 heat or cold possibly, for physical reasons, associated with 

 a particular colour. A compensating arrangement has also 

 been attributed to the deaf, and more especially to the 

 deaf-blind. Such notions, however, must be abandoned 

 before the evidence of recent investigations. 



The question is discussed with much shrewdness in a 

 paper on the physiology of the blind, by M. Kunz, director 

 of the Institution for the Blind at Illzach-.VIulhauscn. He 

 refers especially to the observations of Prof. Griesbach, 

 made on a considerable number of blind persons in the 

 Miilhausen Institution, and also, for the sake of compari- 

 son, on pupils in the public schools of Miilhausen of the 

 same age. The results are somewhat surprising. As 

 regards perception of the direction of sound, there is no 

 difference between the seeing and the blind. The average 

 distance at which sounds could be heard was essentially 

 the same in both classes. As tested by Zwaardemaker's 

 olfactometer, the delicacy of the sense of smell was rather 

 in favour of the seeing. Griesbach used his own resthesio- 

 meter, with parallel pins on springs, instead of the old 

 Weberian method with compasses, in testing the acutencss 

 of touch, with the result that the average minimum 

 distance, say on the tip of the forefinger, &c., at which 

 two points were felt was greater in the blind than in the 

 seeing ; in other words, that the seeing had a finer sense 

 of touch than the blind. It is generally supposed that the 

 palp of the forefinger of the right hand, which is used by 

 the blind in feeling the points in Braille's system of teach- 

 ing the blind to read, must be very sensitive, but this 

 w'as 'found not to be the case. Too high a degree of 

 sensitiveness to touch is rather unfavourable to discrimin- 

 ating the points in Braille's type, and it is curious that 

 when, in the blind, the epidermis of the skin covering 

 the right forefinger becomes thickened by manual labour 

 or by laborious practice in " reading," the discrimination 

 of the points becomes easier. It was observed, also, that 

 sometimes in the blind there was a difference as regards 

 receiving impressions between the two forefingers. 



There appears to be no evidence, therefore, that blind- 

 ness, ^er sc, increases the sensitiveness of the other senses, 

 but, on the principle that if one sense is defective the 

 others are likely to be also defective, the other senses, in 

 the average blind, are less acute than in the seeing. How, 

 then, are we to explain the wonderful way in which the 

 blind avoid obstacles and find their way about? It has 

 been supposed that by practice the skin of the face, in 

 particular, becomes more sensitive, or, in other words, 

 that the blind habitually pav attention to currents of air 

 playing on their faces, and especially they may be influenced 

 by sensations of temperature. They say that they " know " 

 they are near a wall because they " feel " it, although 

 they do not touch it. It would be interesting to examine 

 the blind as regards the sensitiveness of the hot and cold 

 spots of the skin revealed by Goldscheider and others. 

 The theory of sensitiveness to the direction and tempera- 

 ture of air currents is supported by the observation that 

 the blind do not so readily avoid an obstacle if the face 

 is covered or even if thev are blindfolded. This suggests 



NO. 2054, VOL. So] 



the question : Are all so-called blind people absolutely in- 

 sensitive to light? 



It is also believed that the blind pay an almost involun- 

 tary attention to the direction and quality of sounds. The 

 blind man " taps " his stick. When snow is on the 

 ground the blind have difficulty in avoiding obstacles. 

 One must not forget, however, the psychical element that 

 enters into the question. The effort of attention is super- 

 added to the sensory impression. Impressions may reach 

 the sensorium of which we are usually unconscious, but 

 they may be detected by an effort of attention. This was 

 strongly pointed out by Helmholtz. The senses of the blind 

 are not more acute than those of normal people, but 

 the necessities of the case oblige the blind to pay attention 

 to them. John G. McKendrick. 



The Zoological Position of Tarsius. 



Two years ago (N.^ture, May 2, 1907, pp. 7 and S) I 

 directed attention to the fact that the recent additions to 

 our knowledge of the Primates would compel us to look 

 upon this order as being composed of three diversely 

 specialised phyla of subordinal rank. It seemed clear that 

 we should have to adopt some such subdivision of the 

 Primates as that employed by Gadow (" .^ Classification of 

 Vertebrata," London, iSgS, pp. 52 and 53), who called the 

 three suborders Lemures, Tarsii, and Simia; respectively. 



The researches of Hubrecht had shown that in respect 

 of certain phases in its developmental history Tarsius 

 differs from the lemurs and resembles the apes, and, as 

 the result of the examination of its brain, I had come to 

 the conclusion that Tarsius is much more primitive, and 

 at the same time distinctly more pithecoid, than the lemurs 

 (Linnean Society's Journal, 1903). But Hubrecht would 

 interpret these facts (see Nature, December 24, 1908, 

 p. 229) as a demand for the exclusion of the lemurs from 

 the Primates. The memoirs published within recent years 

 by Forsyth Major, Earle, Standing, and the writer have 

 made it perfectly clear that the demonstration of the 

 affinities of Tarsius to the apes does not in any way affect 

 the recognition of the fact that it is at least as nearly 

 related to the lemurs, so that Hubrecht's proposal to 

 restrict the term Primates to Tarsius and the apes lacks 

 any adequate justification. 



At the last meeting of the British Association I pointed 

 out that the results of stimulation of the brain in lemurs 

 and the examination of the distribution of the histologically 

 distinct cortical areas by Page May, Wilson, and myself, 

 had revealed a close resemblance to the condition found 

 in the apes. In opposition to the views of Vogt, Brod- 

 niann, Halliburton, and Mott, we found that a true sulcus 

 of Rolando — which is peculiarly distinctive of the Primates 

 — showed a tendency to develop in every prosimian family, 

 and that in the lemur Perodicticus the morphology of the 

 cerebral hemisphere is identical in almost every respect 

 with that of the .\merican monkey Pithecia. These facts 

 bear unmistakable witness to the right of the lemurs to be 

 included in the Primatijs. 



In a monograph on the human hair by Friedenthal, a 

 curious distinctive feature of the distribution of the hair 

 in the Simire is mentioned. This author states that in 

 man and all the other Primates (among which he does iwt 

 include the lemurs) the sole of the foot is absolutely devoid 

 of hair, not only in the adult, but also in the fcetus, and 

 the line of demarcation between the hairless and the hairy 

 skin runs across the back of the heel ; but in the Prosimiae 

 the posterior part of the sole of the foot is coated with 

 hair. I have examined a series of specimens of Tarsius 

 given to me by Dr. Charles Hose, and find that in the 

 manner of distribution of the hair on the foot Tarsius 

 differs from the apes and agrees with the lemurs, .^t a 

 time when so much weight is being attributed to facts of 

 relatively slight signilicanre on the other side, it seems 

 worth pointing to this curious straw of evidence, which 

 shows that, as the Primate stream flowed from its source 

 among a group of Tarsius-like mammals, the apes and the 

 lemurs were merely divergent branches of this stream, and 

 that the latter suborder, although definitely specialised in 

 structure, remained nearer to the Tarsii than the apes. 



Cairo, February 17. G. Elliot Smith. 



