PHYSIOLOGY. 



585 



distinguished viz., a lower, subcortical, or reflex 

 set called into play by impressions of hearing, 

 vision, or other special senses; and a higher, cor- 

 tical set, concerned with conscious, arbitrary 

 motion. 



The sheath of Schwann of medullated nerves 

 has been shown by Dr. A. Gurrtsch to be genet- 

 ically an exogenous and quite foreign mesodermal 

 formation. The observation was made that it 

 did not in the first instance closely embrace the 

 medullary sheath, but that the space between the 

 two was gradually filled up by the growth in 

 girth of the axis cylinder and of the medullary 

 sheath. 



Special Senses. A case of the cerebral lesions 

 observed in an instance of complete acquired 

 color blindness while achromatic vision was re- 

 tained is described by Dr. George Mackay and 

 Dr. J. C. Dunlop, of Edinburgh. The patient, a 

 man of great mental capacity, sixty-two years 

 of age, whose color sense had always been good, 

 and who especially appreciated the bright colors 

 of flowers, having become anaemic, all at once 

 experienced serious defects in his eyesight, find- 

 in" himself unable to read his letters or to recog- 

 nize vivid colors in some children's dresses. On 

 examination, Dr. Dunlop found him completely 

 color blind, while his distant form sense was 

 good. The external aspect of his eyes was natu- 

 ral, but every color appeared gray to him. The 

 diagnosis was double homonymous hemianopsia, 

 complete for color sense, incomplete for form sense 

 about the point of fixation. During the two 

 months following the examination the patient ac- 

 quired greater facility in reading, but had no- 

 restoration of his color sense. In a little less 

 than four months from his attack he suddenly 

 developed a right-sided hemiplegia, and in five 

 days afterward died. The post-mortem examina- 

 tion disclosed an atrophy of the temporal occipi- 

 tal convolution on both sides, affecting the lower 

 edge of the occipital radiation. This atrophy 

 Mas found to be due to a hyaline degeneration 

 of the adventitia of the vessels, which had to a 

 great extent cut off the blood supply, and had 

 led to complete destruction of the proper ele- 

 ments, both fibers and cells, of the affected por- 

 tions of the brain. The authors remark that in 

 this case the total loss of color sense was asso- 

 ciated with a bilateral lesion of the fusiform con- 

 volution so well defined and symmetrical that it 

 is difficult to avoid the conclusion that the gray 

 matter of that convolution is probably concerned 

 in the perception of colors. 



While until recently the smallest lateral dif- 

 ference of place that is just perceptible by vision 

 has been given as from about 50" to 1' angular 

 measure, Prof. George M. Stratton, using a modi- 

 fied method, has found that lateral difference of 

 place of about 7" can be directly perceived. In 

 the old method of determination, employed by 

 Helmholtz and others, two parallel lines were 

 brought together until they were just finally dis- 

 tinguished as two. In the experiments of Prof. 

 Stratton, instead of using lines or points side by 

 side, lines were so arranged end to end that the 

 upper of two perpendiculars could be moved at 

 will to the right or left, while still remaining 

 exactly parallel to the lower line. The observer 

 had simply to judge whether the upper line was 

 continuous with the lower line, or to which side 

 it was displaced. The result, which gives 7" as 

 the limit of space distinction under these condi- 

 tions, is interesting as explaining the experi- 

 ments of Bourdon, according to which a differ- 

 ence of position amounting to only 5" gives a 



rceptible stereoptic effect. 





In a study of the effects of repeated detona- 

 tions on the ear, made during the tiring at a 

 camp in Natal, the German Dr. Miiller examined 

 96 tympanums before and after the exercise. 

 He observed notable alterations in 44 cases. 

 Seven times multiple hemorrhages were remarked, 

 manifesting themselves as minute droplets of 

 blood, the How in one case being as large as a 

 lentil. In 37 other cases there was merely a 

 diffused, more marked redness on the margin 

 of the tympanum. As a rule, the ears on which 

 alterations were remarked had been previously 

 not quite normal. With 40 subjects the distance 

 at which the tuning fork was heard was dimin- 

 ished. Rinne's test always gave positive results. 

 In 26 cases words spoken in a low tone were not 

 heard at 8.6 metres, the normal mean. Only four 

 subjects complained of hummings and tinklings. 

 The author believes that serious lesions are ex- 

 tremely rare with men who perform their two 

 years of service. On the other hand, officers and 

 underofficers whose duty it is to give instruc- 

 tion in firing during long periods often become 

 partially deaf, and are afflicted with hummings. 

 Retraction and bluntness of the tympanum are 

 detected in such cases. Dr. Miiller draws the con- 

 clusion from his experiments, that only men with 

 perfectly sound ears should be received in the 

 artillery. 



The experiments of Weber on the least observ- 

 able differences in the action of weight as inter- 

 preted by sensation led to the conclusion that 

 to obtain an observable difference in sensation 

 we must always add one third. Fechner, assum- 

 ing that the increase is always the same pro- 

 portionately, deduced the Weber-Fechner formula 

 for stating the relation of stimulus to sensation in 

 quantitative terms, which may be thus expressed. 

 To obtain an arithmetical series of sensations a 

 geometrical series of stimuli is required. To 

 give the former, equal increments of sensation are 

 added; to obtain the latter, we must multiply 

 the successive stimuli by the common factor. 

 C. Lloyd Morgan, finding that the results of a 

 large number of carefully conducted observations 

 were not in accordance with this formula, has 

 made continued studies of the subject, which 

 are described in the Psychological Review and 

 in Nature. From them he deduces a modification 

 of the Weber-Fechner formula as follows: For 

 constant increments of sensation the concomi- 

 tant increases of stimulation are in geometrical 

 progression. This differs from the Weber-Fech- 

 ner formula in that it assigns the geometrical 

 progression to the successive increments of 

 stimulus. 



Miscellaneous. Researches by Prof. F. T. 

 Paul on the development of dentine confirm the 

 view that the process is practically similar to the 

 formation of bone in membranes. Among the 

 points brought to light is the fact that the young 

 pulp contains a complete fibrous basis composed 

 of delicate wavy fibers interlacing in every direc- 

 tion. These fibers are found to be directly de- 

 rived from the cells, and are of a gelatin-yield- 

 ing character. It is also shown that the first 

 layer of cells found on the surface of the pulp 

 beneath the ameloblasts are not odontoblasts, 

 but develop into fibers, and on the actual surface 

 these fibers blend together and form a membrane 

 which lies iust beneath the ameloblasts. The 

 odontoblasts make their appearance subsequent- 

 ly, and insert themselves, as it were, between 

 these fibrous surface cells, the nuclei of the latter 

 undergoing atrophy. The odontoblasts are repre- 

 sented as being invested with a complete net- 

 work of fibers derived from the connective tissue 



