PHYSIOLOGY. 



C91 



Also, that relaxation occurs with very much 

 greater rapidity than actual accommodation; 

 that, with two eyes of much the same refract- 

 ive character, the accommodation velocity of 

 either, measured separately, is about the same 

 as that of the two acting in concert; and that 

 in the present state of knowledge no absolute 

 data can be given as to the time occupied by 

 the action of the local mechanism for any given 

 distance. 



Describing his experiments on the depend- 

 ence of visual acuteness on light-intensity, Dr. 

 Uhthoff remarks that differences among the 

 eyes examined showed themselves specially un- 

 der weak light-intensities, and that the mini- 

 mum of visual acuteness (one thousandth of 

 the normal value) was, in particular cases, still 

 observable with the removal of the petroleum- 

 lamp to the distance of 360 metres. The visual 

 acuteness was further examined under a chang- 

 ing intensity with red and blue light. Red 

 light, just as much as white, showed with in- 

 creasing intensity a very rapid increase of 

 visual force. The curve in the case of red 

 light was, however, different from that in the 

 case of white light. Under a blue light the 

 visual sharpness very slowly declined with in- 

 creasing light-intensity. 



Kollmann, from his examinations of the tactile 

 apparatus of the foot of man and of the apes, 

 has reached the conclusion that remarkable dif- 

 ferences exist between the two in all the parts 

 differences, moreover, that are much more 

 marked in the lower forms than in the anthro- 

 poid apes. In the lower apes (chiromyida and 

 lemurs) the cutaneous ridges lie on a thick bed, 

 and run almost longitudinally to the nails, from 

 which they are separated by a few arches only. 

 In the other lower apes these parallel longitu- 

 dinal gyri are only found in the middle of the 

 pulp or tips of the fingers, which are termed 

 the tactile balls of the first order ; more peri- 

 pherically, the central straight fasciculi come to 

 be surrounded by elliptic and more circularly 

 arranged ridges. This last arrangement, which 

 is usual in the lower apes, recurs also in the 

 higher anthropoid apes in the tactile balls of 

 the first order. Certain types as the sinus 

 obliquus, the stria centralis longitudinalis, the 

 vortex duplicatus, and the circulus all similar 

 to those described in man, occur in the higher 

 apes. In the form of the tactile balls of the 

 second order (situated in the sole of the foot, 

 at the base of the intercligital spaces), and in 

 those of the third order (situated on the thenar 

 and hypothenar eminences), the anthropoid 

 apes resemble man more closely than the lower 

 apes. The lines of these balls often form sinu- 

 ous rings in man, or at least completely closed 

 figures ; but full circles, such as are seen in the 

 lower apes, except that one which is situated 

 just behind the thallux, have not^been seen in 

 him. The human foot has but one tactile ball 

 of the third order, and that is situated on the 

 fibular side ; in most apes there is one on the 

 tibial side also. In both man and apes the 



tactile balls are more sensitive than the adjoin- 

 ing parts. 



Herr Aronsohn, studying the physiology of 

 the sense of smell, has found that the small- 

 est quantities of clove-oil and bromine, which 

 dissolved in 0-6 per cent, of common-salt so- 

 lutions, he was yet able to srnell distinctly, 

 tallied very well with the most minute quanti- 

 ties which Valentin had found perceptible by 

 the sense of smell in the air. By electrical 

 stimulation of the olfactory nerve he had also 

 been able to call forth distinct sensations of 

 smell in some other persons. The physiologi- 

 cal common-salt solution of the temperature 

 of 40 0. had been previously found by him 

 to be entirely indifferent to the olfactory 

 nerves. Were a part of the common salt re- 

 placed by other salts, then, according to the 

 nature of the salt, different, mostly somewhat 

 large, quantities of the salt (osmodic equiva- 

 lents) had to be taken in order to form an in- 

 different solution. He had now exactly deter- 

 mined these osmodic equivalents for a series of 

 salts. Finally, in order to demonstrate that 

 there were special fibers in the olfactories for 

 special smells, he had dulled his own sense 

 for a certain quality of odors, that, namely, of 

 sulphuret of ammonium, and had convinced 

 himself that, though no longer able to perceive 

 this smell, he was yet very well able to srnell 

 ethereal oils. 



Prof. John B. Haycraft has described before 

 the London Physiological Society some experi- 

 ments with the sense of touch, which were 

 made with especial reference to the quality of 

 roughness. It is generally supposed that, al- 

 though the eye is only capable of perceiving 

 separately some fifteen or twenty stimuli in a 

 second, a far greater number may be applied 

 to the ear or the skin, and be heard and felt, 

 each by itself. Helmholtz has been gener- 

 ally misquoted, and the statement that 132 

 " beats " a second can be separately heard, 

 continually appears in the text-books. Still 

 more absurd is the assertion that^ 1,400 im- 

 pacts of a toothed wheel may be separately 

 felt. In point of fact it is found in every case 

 that 20 or 30 impacts are fused together. 

 When from 30 to 1,400 impacts fall upon the 

 finger-tip, we are conscious of a feeling of 

 "roughness." We know by the aid of sight 

 that this sensation is due to rapid tactile stim- 

 ulation, but by nothing in the sensation itself. 

 Rapid beats produce in like manner a rough 

 sound, the cause of dissonance in music. In both 

 cases the " rough " sensation varies in quality, 

 becoming of a finer roughness with more rapid 

 stimulation. This cause of the sensation can 

 not be analyzed any more than with a sensation 

 of redness, except by experiment and the use 

 of the other senses. Thus, the sensation pro- 

 duced by 132 beats per second is recognized as 

 being caused by rapid beats only, because the 

 experimenter has traced the continuity of his 

 feelings from a point where the intermittent 

 character of the cause was evident. The sen- 



