G68 



PHYSIOLOGY. 



>rtunity of testing the sensitivity of the 

 skin of a man who had had his left forearm in- 

 cased in plaster of Paris for a period of three 

 months. During this entire period the forearm 

 could not be moved either at the wrist or at the 

 elbow. Prof. Krohn compared the sensitiveness 

 of the skin of the uninjured right forearm with 

 that of the left forearm of the same person, after 

 the plaster-of-Paris case had been removed, by 

 means of the usual a?sthesiometric tests. He 

 found that on the latter forearm, the one so long 

 immovable, when the two points of a pair of 

 dividers or compasses, touching the skin at a 

 given locality, were separated by as much as 55 

 millimetres, they were felt as one instead of two ; 

 while on the rig'ht forearm they had to be only 

 20 millimetres apart in order to be perceived as 

 two. On the back of the left arm, at a different 

 locality from that just mentioned, it was found 

 that even when the two points of the dividers 

 were 75 and 80 millimetres apart they were felt 

 as one ; while at a corresponding locality on the 

 right arm the skin was so sensitive that points 

 not more than 17 millimetres apart could be felt 

 as two. The skin of the subject of the experi- 

 ment was equally sensitive on both arms before 

 he met with the accident that led to the casing 

 of one arm in plaster. Prof. Krohn thinks, there- 

 fore, that the sensitivity of the skin over the in- 

 jured forearm was lost simply because that 

 member was for so long a time immovable. The 

 author points out that the experiment has an 

 important bearing upon the principle that " the 

 localizing power is delicate in proportion as the 

 skin covers a movable part of the body." 



The result of an extensive series of observa- 

 tions in which the reaction time was measured 

 for sight, hearing, and touch is reported by 

 Prof. Rutherford. The stimulus for the ear was 

 the response of a telephone to a current, that for 

 the eye the movement of an electro-magnetic 

 signal, and that for the touch an induction cur- 

 rent sent through the skin, the stimulus in all 

 cases being made by the closure of a circuit. 

 The response of the individual was the break of 

 a current sent through a suitable electro-mag- 

 netic recording arrangement. By means of the 

 pendulum large series of records were obtained, 

 in which, as the initial starting-point occurred 

 ill ways at one place, and the different observa- 

 tions were arranged in series beneath one an- 

 other, a comparison between different reaction 

 times was rendered very conspicuous. The au- 

 thor found that with 8' intelligent men of ages 

 varying from nineteen to sixty-two years the 

 time for sight varied from T^ to -^ of a sec- 

 ond; for hearing, -,^ to ^; for touch, -fa to 

 Vfi',,. The shortest reactions were obtained when 

 ihe response was the hand on the same side of 

 the body as the ear or cheek that was stimu- 

 lated. 



Investigations have been made by Prof. C. S. 

 Dolley and Prof. J. ]\I. Cnttell for determining 

 the conditions thai affect the length of reaction 

 times on dermal stimuli, and for the study of the 

 application of the reaction times to the meas- 

 urement of the velocity of the nervous impulse 

 in motor and sensory nerves. For the applica- 

 tion of the stimuli two points were chosen on 

 the arm over the median nerve and two on the 

 leg over the posterior tibial nerve. The points 



on the arm were 30 centimetres apart, and those 

 on the leg 50 centimetres apart, and the length 

 of intervening nerve would be nearly the same. 

 It was found that the reaction times were longer 

 when the stimulus was applied to the lower 

 points on the arm and leg than when points less 

 distant from the brain were used. If the differ- 

 ence in time is really due to the difference in 

 length of the nerve traversed, the velocity of 

 the impulse in the sensory nerve is 21-1 metres 

 and 49'5 metres per second respectively for the 

 two observers. The velocity in the sensory fibers 

 of the posterior tibial nerves was 31 ! metres 

 per second for Prof. Dolley and 64-9 metres per 

 second for Prof. Cattell. 'This large difference 

 between the two observers, however, is attrib- 

 uted to differences in the velocity of the im- 

 pulse in the sensory nerve. In the case of re- 

 action experiments with dermal stimuli the elec- 

 tric shock was mostly used ; but as the physio- 

 logical effects of the shock were found to vary 

 greatly in different parts of the body, a method 

 was devised for applying a touch or a blow. It 

 was found that the same objective force of blow 

 was followed by the same real subjective sensa- 

 tion more nearly than in the case of electrical 

 stimulation. From the difference in the reac- 

 tions on touch when the stimulus was applied 

 to the arm and to the thigh, the velocity of the 

 nervous impulse in the sensory tracts of the 

 spinal cord was determined at about 40 metres 

 per second. 



In the experiments of Prof. Dubois on the pro- 

 duction of heat by hibernating animals, made 

 upon the marmot, section of the cord at the level 

 of the fourth cervical nerve was found to inter- 

 fere with the waking from winter sleep. The 

 delay thus caused was, however, only partially 

 due to the muscular paralysis and consequent 

 inability to produce heat, since it appears that 

 the integrity of the sympathetic system is an 

 essential factor in the process. Further experi- 

 ments indicated that the nervous control of the 

 circulation was necessary for the waking up, and 

 that the most important part of the circulation 

 was that through the liver, which, under the 

 conditions produced by the section, was inade- 

 quate for the supply of that organ. In conse- 

 quence of this inadequate circulation the author 

 believes that the functions of the liver were very 

 much interfered with, and that in the normal 

 animal these functions were at the moment of 

 waking very actively carried on, particularly 

 those by which glycogen is converted into sugar. 



M. d'Arsonval has shown that the excitability 

 of nerves and their power to produce rhythmic 

 contractions in muscle persist as long as ten 

 hours after death. Following out D'Arsonval's 

 experiments, Brown-Sequard found that muscles 

 affected with rigor mortis can contract and relax 

 alternately, though with comparative slowness. 



Special Senses. The researches of Dr. J. S. 

 Risien Russell on eye movements dealt with ocu- 

 lar movements as influenced by cerebral and cere- 

 bellar conditions, the experiments being made on 

 dogs and monkeys. The author found that all 

 the movements of the eyeballs are represented in 

 the cerebral cortex, and not lateral movements 

 only to the opposite side that is, away from the 

 cerebral hemisphere stimulated. The fact that 

 under ordinary circumstances none but the lat- 



