756 



PHYSIOLOGY. 



observed to follow rapid stimulations of me- 

 dium and strong intensity. In a large majority 

 of cases both vaso-constrictor and vaso-dilator 

 fibers were stimulated by the application of 

 electricity to the sciatic nerve. The vaso-di- 

 lator nerves are more irritable, with a slow, 

 and the vaso-constrictor nerves with a rapid, 

 rate of stimulation. With each intensity of 

 stimulation the average result shows, with an 

 increasing rate of stimulation, a greater tend- 

 ency to contraction. "With a slow rate of 

 stimulation, a feeble irritation acts relatively 

 more on the vaso-dilaior and a strong irrita- 

 tion more on the vaso-constrictor nerves. With 

 more rapid stimulation this difference was not 

 noticed. Of the three-named results of elec- 

 trical stimulation, the second contraction fol- 

 lowed by a dilatation is by far the most com- 

 mon. Moreover, this result passes by insen- 

 sible gradations into the first by the disappear- 

 ance of the dilatation, and into the third by 

 the disappearance of the contraction. The 

 first and third results may therefore be regard- 

 ed as particular cases of the second, in which 

 the dilatation and the contraction are respect- 

 ively reduced to zero, and on this supposition 

 the average amount of contraction and of dila- 

 tation can be calculated for all the observations 

 of a given rate and intensity of stimulation. 

 Experiments on the effects of temperature 

 were not sufficient to justify definite conclu- 

 sions, but the results were not so marked as 

 the observations of others had led the authors 

 to expect. The studies of the effect of the 

 varying length of time between the section of 

 the nerve and its stimulation showed that the 

 motor nerve-fibers might begin to show signs 

 of degeneration as early as the second day after 

 section ; and the loss of power was nearly al- 

 ways complete on the fourth day. Probably 

 the degeneration of the motor nerve-fibers fol- 

 lows a similar course to that of the vaso-con- 

 strictors, while that of the vaso-dilators is 

 much slower than either. Investigations of 

 the effects of the vascular contractions and 

 dilatations described upon the blood-supply of 

 the limb resulted in showing that the sciatic 

 nerve contains fibers that exert a very marked 

 influence upon the blood-vessels. Whether 

 these changes occur chiefly in the cutaneous 

 or in the muscular blood-vessels is a question 

 which the experiments afford no data for de- 

 ciding. In the use of the terms u vaso-con- 

 strictors" and "vaso-dilators," the authors 

 do not wish to be understood as expressing 

 any opinion upon the question of the inde- 

 pendent anatomical existence of fibers having 

 these functions. The phenomena observed may 

 be quite as well explained on the hypothesis 

 that there is one set of fibers acting in differ- 

 ent ways under different circumstances. 



Samuel Wilks has made a study of the eymp- 

 tom of sudden falling, in which he finds illus- 

 tration of the fact recently accepted by clinical 

 students that a much more intimate connec- 

 tion exists between the nerve-centers, nerve- 



fibers, and muscles than had before been con- 

 ceived. If a patient is subject to falling, it is 

 evident that the higher motor regions, or some 

 part of the lower track leading to the mus- 

 cles have, for the moment, become inert, and 

 we ask ourselves in what way this has been 

 brought about. It is known that the function 

 of the brain is dependent directly upon a due 

 supply of blood, and that if the circulation be 

 arrested unconsciousness occurs instantly and 

 the person falls, and a general cessation of the 

 circulation would result in the loss of other 

 functions of the brain than that of conscious- 

 ness; but it does not follow that there might 

 not be an arrest to the flow of blood in some 

 portion of the brain, leading to a paralysis of 

 certain muscles without loss of consciousness. 

 It is now generally believed that an inhibitory 

 action can be produced on the different organs 

 of the body through the nervous system, and 

 that the brain can be included under the gen- 

 eral law; and it may be a question whether 

 some direct influence may not be exerted 

 through the nerves, either on the heart or the 

 brain. The author has taught that pressure 

 on the neck, as in hanging or garotting, will 

 often produce instantaneous insensibility and 

 death ; and that strangulation by no means im- 

 plies congestion of the lungs and engorge- 

 ment of the right side of the heart. That the 

 brain can be acted on directly independent of 

 the heart, would seem to be proved by cases 

 of shock, whether physical or moral. In fa- 

 vor of this view may be mentioned the case ot 

 wild animals suddenly expiring from fright, 

 and the lesser effects produced upon them by 

 the so-called mesmeric process. Many in- 

 stances might be mentioned to show how di- 

 rectly the healthy working of the muscles is 

 under the influence of the brain, and that the 

 activities of the two structures correspond. 

 The possible agency of the spinal cord also de- 

 serves attention, for, seeing that the fibers of 

 the motor tract proceed from the brain mostly 

 to the anterior cornua of the cord, and from 

 these again other nerves pass on, which stim- 

 ulate the muscles, it is probable that nearly all 

 the cerebral influence is conveyed through 

 the spinal system. The author infers that the 

 cord may be the seat of an inhibitory influence 

 from the fact that, in some cases of very 

 chronic spine-disease, patients have suffered, 

 among their earlier symptoms, from sudden 

 falling. When falling occurs, with loss of con- 

 sciousness, the cause may be placed in the 

 brain proper ; when there is no loss of con- 

 sciousness, it is looked for in the motor tracts 

 below, or in the spinal centers. 



Special Senses. MM. Charpentier and Pari- 

 naud, working independently, have concluded 

 that visual sensations involve two distinct 

 kinds of physiological processes. Sensations 

 of one kind are " photesthetic," and comprise 

 luminous sensations pure and simple, merely 

 discriminating light in distinction from dark- 

 ness. The other sensations are truly " visual," 



