PHYSIOLOGY. 



669 



eral movements to the opposite side can be 

 elicited on excitation of the one cerebral hemi- 

 sphere is explained by Dr. Hughlings Jackson and 

 the author as resulting from the superior power 

 of those movements, by which the others are 

 overcome. When this movement is excluded, 

 other movements can be evoked which are not 

 apparent under the usual conditions. When abla- 

 tion of part of the center for con jugate turning of 

 the eyes was performed, the first effect was the es- 

 tablishment of a position of the eyeballs in which 

 they both turned toward the injured cortex; 

 but' this condition was recovered from in a few 

 days. When the animal, after the eyes had re- 

 turned to their normal position, was placed under 

 anaesthetic influence, the abnormal position which 

 originally resulted from ablation of part of the 

 eye area of one cerebral hemisphere was again 

 assumed. Certain control experiments made it 

 evident that under normal circumstances the 

 cerebral centers in the two hemispheres do not 

 succumb simultaneously under narcotic influ- 

 ences. The experiments give reason for suppos- 

 ing that ocular deviation after ablation of part 

 of the cerebellum is a paralytic rather than an 

 irritative phenomenon. The nystagmus result- 

 ing from ablation presents two different phenom- 

 ena. The one is spontaneous and probably an 

 irritation phenomenon, possibly reflexively in- 

 duced ; and the other is only momentarily evoked 

 on voluntary movements of the globes, and is in 

 all probability a paralytic phenomenon, due to 

 weakness of the muscles producing the move- 

 ment of the eyes in any given direction. The 

 mechanism of the nystagmus that has been re- 

 covered from and reappears under the influence 

 of an anaesthetic is not easy to explain, but the 

 author is inclined to class that form as a para- 

 lytic one. The effects obtained after ablation of 

 parts of the cerebellum are not dependent on any 

 interference with the labyrinth and eighth nerve. 

 The experiments show that the influence exerted 

 on the ocular muscles of the opposite eye by one 

 lateral lobe of the cerebellum and the cortical 

 cells of the eye area of the cerebral hemisphere 

 on the same side as the lateral lobe of the cere- 

 bellum antagonize each other, and that the 

 cerebellum exercises an independent action on 

 the ocular muscles, with a direct influence, and 

 not one brought about indirectly through the 

 agency of the opposite cerebral hemisphere. 



Dr. C. S. Sherrington finds that in the monkey, 

 an animal in which the optic axes are parallel, if 

 the third and fourth cranial nerves of one side 

 the left, for example have been severed, so that 

 the rectus externus remains the only unparalyzed 

 ocular muscle, appropriate excitement of the 

 cortex cerebri produces conjugate movement of 

 both eyes toward the opposite side that is, from 

 left toward right the left eye traveling, how- 

 ever, only so far as the median line. Inhibition 

 of the tonus and of the active contraction of 

 rectus externus can thus be elicited from the 

 cortex. The reaction is obtainable from all that 

 part of the cortex which on excitation gives con- 

 jugate lateral deviation of the eyes. The au- 

 thor's observations show that at least in many 

 cases the action of arrest takes place in subcor- 

 tical centers, and that the cortex is not essential 

 to it. Inhibition is found to occur in volitional 

 lateral deviation as well as under experimental 



excitation, but less perfectly. In two animals 

 which had fully recovered from the operative dis- 

 turbance, if the gaze was attracted to an object 

 held level with the eyes and to the right of the 

 median plane (third and fourth nerves cut) the 

 left eye looked straight forward, the right eye 

 looked to the right. If the object was then 

 shifted more to the right or less to the right, the 

 right eye followed it, moving as the object was 

 moved, while the left eye remained motionless, 

 looking straight forward all the time. When 

 the object was shifted farther and farther to 

 the left both eyes followed it with a steady con- 

 jugate movement not visibly different from the 

 normal. When the object was carried from the 

 left-hand verge of the field toward the median 

 plane both eyes followed it accurately as before. 

 If the object was moved suddenly from the ex- 

 treme left-hand edge of the field up to the 

 median plane both eyes immediately and appar- 

 ently with equal quickness reverted to parallelism 

 with that plane. Or, if the object were suddenly 

 brought back from the left edge of the visual 

 field to some point intermediate between that 

 and the median plane, both eyes at once shifted 

 apparently with equal quickness to a correspond- 

 ingly diminished deviation from the primary 

 position. These actions must mean that in the 

 left eye relaxation of the rectus externus kept ac- 

 curate time and step with rectus externus of the 

 right eye ; and the action of the left rectus ex- 

 ternus gives presumably a faithful picture of a 

 synchronous process going forward in the right 

 rectus internus. The author has also seen this 

 inhibition in some forms of nystagmus. The 

 muscles which open and close the palpebral 

 aperture afford another case in which antago- 

 nistic correlation may be examined. 



Muscular System. In his study of the time 

 relations of the voluntary tetanus in man David 

 Fraser Harris found that in the adult human 

 being this is an "incomplete" tetanus, there 

 being on an average 12'5 contractions a second, 

 with a minimum of 6 and a maximum of 18. In 

 the majority of instances the tracing of the vol- 

 untary tetanus is more distinctly wavy at the 

 beginning than at the end of the continued con- 

 traction that is to say, the wave apices are at 

 the commencement much more discernible and 

 therefore more easily counted. The muscu- 

 lar effort, rises very rapidly to its maximum of 

 force, and the average rate of the tetanus is 

 higher at the beginning of the effort than at the 

 end. A portion of the author's work corrobo- 

 rates the statement that the average rate of single 

 voluntary muscular twitches as. for example, 

 shaking one of the fingers as quickly as possible, 

 shaking (imitating shivering of) the whole arm 

 and hand, etc. is 10 or 11 a second; a figure 

 sufficiently near to that of the rate of the volun- 

 tary tetanus to be reckoned identical with it. 

 Schafer and Horsley have proved that the 

 " rhythm of muscular response to electrical 

 stimulation (faradization) of nerve centers is the 

 same whether the excitation be applied to the 

 gray matter of the cerebral cortex, to the fibers 

 of the corona radiata, or to the spinal cord (but 

 not to the peripheral motor nerves) ; the rate of 

 the rhythm is not the same as that of the excita- 

 tion, except when the frequency of excitation is 

 10 per second or less ; and with all higher rates 



