I. Physiological Journals, &c.

I. Physiological Journals, &c.[33]

Rate of Current in Sensory Nerves.—Bloch has recently made a very elaborate experimental inquiry into the rapidity of the nerve current in sensory nerves, and has arrived at conclusions differing from those of other physiologists.(10 § 1, item 1 ¶ 1)

(1) The rapidity of the nerve current in sensory nerves should be determined exclusively by sensations, without involving any other physiological phenomena.(10 § 1, item 1 ¶ 2)

(2) Bloch's method is founded upon observations of the greater or less persistence of the sensation between two successive shocks. If two shocks are received simultaneously or successively, one by each hand, then in the latter case, if the interval between the two shocks be sufficiently short (1/45 of a second being the limit) the mind perceives only one sensation.(10 § 1, item 1 ¶ 3)

(3) The explanation of this is that the sensation produced by the first shock lasts with a sufficient degree of intensity until the arrival of the second impression and the commencement of the second sensation. By graduating the distance between the points of shock and graduating the time between successive shocks the sensations may still be synchronous, although the points of shock are widely apart. If we keep the same time between shocks at different points of shock, the interval between the sensations or the absence of synchronism will indicate the time occupied by the sensory transmission.(10 § 1, item 1 ¶ 4)

(4) If the first shock be transmitted, say to the lobule of the nose (nearer the sensorium), and the second to the hand, the synchronism between the two shocks becomes evident on permitting a longer time to elapse between the two shocks than when the shocks are sent to both hands. The time of receiving the shock and of the sensation is registered upon a rapidly revolving wheel. The difference between the two intervals measures the difference of the duration of the transmissions from the hand and from the nose respectively to the sensorium.(10 § 1, item 1 ¶ 5)

(5) Bloch found by observation and subsequent calculation that rapidity of transmission is greater in the spinal cord than in the nerves.(10 § 1, item 1 ¶ 6)

(6) Experiments made by stimulating the nose, the hand, and the foot have given the following results: rapidity of the nerve current in the Spinal Cord is 194 metres per second; in the Nerves, 132 metres per second.(10 § 1, item 1 ¶ 7)

The methods previously adopted by physiologists for the measurement of the rapidity of the current of sensory nerves by means of such an apparatus as Regnault's chronograph have given a lower rate than that computed by Bloch. They are--94 metres per second (Kohlsrausch), 60 (Helmholtz), 34 (Hirsch), 30 (Schelske), 26 (de Jaager), and 41.3 (von Wittich). Bloch also states in his paper, (1) that a voluntary movement excited by s sensation and executed by a contraction of the muscles of the forearm and hand is more rapid when one of the two hands is excited than when any other part of the body receives the impression; (2) that flexion of the finger in response to a shock transmitted to the forearm or to the face is produced more slowly than when the shock is transmitted to the hand; and (3) that the general position of the body influences the results and modifies the time required for the transmission of sensory impressions. (Gazette Médicale de Paris, Juin, 1875; Archives de Physiologie, Brown-Séquard, Charcot, Vulpian, Août et Sept. 1875.)(10 § 1, item 1 ¶ 8)

Sleep.--Obersteiner states that sleep is due to the accumulation of acid products in the brain. It is well known that activity in the muscles or nerves is accompanied by the formation of acid substances; but Obersteiner has not proved (1) that the grey matter of the brain during action becomes more acid than it is normally; nor (2) that the presence of acid in the grey matter would so interfere with its activity as to produce sleep. This theory of sleep is, therefore, not based on a sufficient number of facts. (Archiv. f. Psychiatrie, Bd. 29.) Gscheidlen has shown that the grey matter of the brain and cord and of ganglia is always normally acid, whereas the white or conducting matter is neutral. (Pflüger's Archiv, VIII. 172.)(10 § 1, item 2 ¶ 1)

Pflüger has recently advanced a remarkable physico-chemical hypothesis regarding sleep, which may be shortly summarised as follows. The functional activity of a nerve-centre, as of any other organ, depends upon the dissociation of living matter, so as to form simpler compounds. This living matter consists of a modified kind of albumen, which is split up into numerous compounds, including carbonic acid. By this process energy is liberated or transformed into heat. An atom of carbonic acid is thrown into a state of very active vibrations, and these vibrations, or explosions, as termed by Pflüger, are transmitted in various directions along the nerves. Deprive a frog of oxygen and it passes into a state precisely resembling sleep or apparent death; admit oxygen and it is again aroused. From this Pflüger infers that a certain proportion of intra-molecular oxygen in the nerve-centres is essential to the waking state, since it secures a certain number of explosions, caused by its union with carbon, to occur in a certain unit of time at a given temperature. But during waking in the process goes on too rapidly, and the energy of chemical affinity is used up much faster than the intra-molecular oxygen of the grey matter of the brain can be replaced. Consequently less and less carbonic acid is formed; fewer explosions occur; and when these sink below a certain number per unit of time sleep occurs. The energy of the brain then sinks so low that it becomes incapable of maintaining action without an adequate stimulus, but even during sleep the brain energy is never entirely lost. Pflüger applies this ingenious hypothesis to periodicity of sleep, and he compares ordinary sleep with the hibernating conditions of mammals during winter and the summer sleep of tropical amphibia. (Pflüger's Archiv, X, 8, 9.)(10 § 1, item 2 ¶ 2)

Hereditary Transmission of Injuries to the Nervous System.—In the Lancet of January 2nd, 1875, Brown-Séquard illustrates the following examples of hereditary transmission: 1. Development of epilepsy in animals born of parents which have been made epileptic by section of part of the spinal cord, or of the sciatic nerve. 2. Change in the form of the ear of animals born of parents which had presented a like change after section of the great cervical sympathetic. 3. Partial closure of the pupil in the descendants of animals in which the pupils had become contracted afte section of the cervical sympathetic or removal of the superior cervical ganglion. 4. Protrusion of the eyeball in the young of animals in which the eye had become prominent from lesion of the restiform bodies. 5. Congestion and gangrene of the ears of animals the parents of which had the same lesion following irritation of the restiform bodies near the point of the calamus scriptorious. 6. Absence of the claw from certain of the toes of the posterior extremity in animals the parents of which had the posterior extremity rendered insensible by section of the sciatic or crural nerves.(10 § 1, item 3 ¶ 1)

These experiments are of great importance as bearing on the question of hereditary transmission of peculiarities acquired even in one generation.(10 § 1, item 3 ¶ 2)

The Accomodation of the Ear for musical tones of different pitch.—Lucae, by otoscopic observations and experiments, has come to the conclusion that the ear possesses two muscular arrangements for accomodation purposes. The ear, he states, is arranged for the reception of low tones by the action of the tensor tympani muscle, and for high tones by the stapedius. The range of action of the tensor tympani rises as high as Cb=9192 vibrations per second. Above that it exercises no influence; but the higher tones are heard with greatest distinctness when the stapedius muscle is in action. When his muscle is relaxed the higher tones are weakend or completely extinguished. These statements are founded chiefly on an ingenious experiment made first by Fick, and since frequently repeated by Lucae. The movements of the membrane of the drum cannot usually be seen by the naked eye in the uninjured living head. To render the movement apparent the teeth are placed gently together, and a glass tube having in the stem an index of coloured fluid (like that of a maximum or minimum thermometer) is placed in the external auditory meatus, having one end in contact with the membrane of the drum, and air tight. On contracting the muscles of the jaw the index moves toward the ear, in consequence of the rarefaction caused by the inward movement of the drum, produced by the simultaneous contraction of the tensor tympani with the muscles of the jaws. When this occurs the deep tones are heard more distinctly than usual. To obtain simultaneous contraction of the stapedius, Lucae caused contractions of the muscle around the orbit (orbicularis palpebrarum) which is supplied by the same nerve as the stapedius. When the stapedius was in action, then high tones are heard more distinctly. Lucae also found, on examining in this manner many individuals, that there were some whose ears appared to be better adapted for hearing high tones than low tones, and vice versâ. He divides all into deep-hearing and high-hearing, and he states that abnormal deep hearing is more distinct in cases of facial paralysis (paralysis of the portio dura--facial nerve), while abnormal high hearing usually occurs where injury and possible loss of substance of the membrane of the drum has been caused by suppuration in the tympanum. In both of these cases the power of accommodation appears to be lost. (Centralblatt, October, 1875.)(10 § 1, item 4 ¶ 1)

John G. McKendrick.

10 § 1 n. 1. Any monographs or journals containing information as to researches into physiological questions bearing on psychology may be sent to the Editor for future notice under this heading.