THE RELATION OF THE ELECTRICAL TO THE MECHANICAL REFLEX RESPONSE IN THE FROG; WITH A SUGGESTION AS TO THE SIGNIFICANCE OF LOVÉN'S ACTION‐CURRENT RHYTHM IN STRYCHNINE PREPARATIONS

Abstract

Records taken, consecutively or simultaneously, of the electrical and mechanical reflex responses of decerebrate strychnine frogs show that a reflex contraction outlasts its electrical counterpart by one‐ or two‐tenths of a second at least, so that when the action of the drug is so slight that the reflex contraction is hardly longer than a twitch, its electrical counterpart terminates as much as 0·05 to 0·1 sec. before the muscle has even shortened to its greatest extent.When the reflex contraction is steadily maintained for over half a second, its electrical counterpart in any sample spot of the muscle may be either continuously maintained (galvanometric) negativity for the same length of time less the one‐ or two‐tenths of a second; or this negativity may be interrupted at intervals, recurring with a frequency of about 10 a second and each lasting four‐hundredths of a second or less. A tremor is apt to occur in the contraction when the interruptions last longer than 0·04 sec., the more readily the smaller the amount of the otherwise maintained negativity. When the interruptions last as long as 0·15 sec. the mechanical response tends to become clonic. During each interruption, any sound spot of muscle may still be negative to a devitalised spot, may re‐attain its electrical status quo, or may become more positive than it was originally to the devitalised spot.The electrical reflex responses of muscles which serve as extensors, especially those which serve mainly as such, may begin with a transient positive variation, usually lasting for about a hundredth of a second when the stimulus is a single instantaneous one. This has been found to occur in the responses of the gastrocnemius muscle only immediately after decerebration of the frog; but it occurs in those of the triceps femoris long after decerebration, and therefore when there is no reason to suspect any abnormal condition of tonus. It occurs in more preparations than not in the triceps in response to excitation of the same‐side brachial nerve, and in as many as not to that of the crossed brachial nerve; and it occurs whichever of the three drugs, strychnine, phenol, or caffein, has been used for raising the excitability of the cord. With two preparations in which the positive variation was found to last over 0·04 sec. the mechanical responses (of the gastrocnemius) began with, or was mainly, relaxation instead of contraction.When the records of the electrical reflex responses of strychnine preparations, taken in turn with a flexor and an extensor muscle acting on the same joints, both show interruptions of a more or less maintained negativity, they show that an interruption often occurs in the response of the one muscle at the same time‐interval after excitation as a return to negativity, or to stronger negativity, in that of the other. This suggests that Lovén's action‐current rhythm, that which occurs as the result of interruptions of the negative variation, indicates a condition of the preparation in which reciprocal. innervation of antagonistic muscles is in force, even when this is not to be detected in the mechanical responses of the muscle; and that in those stages only of the action of strychnine in which there is no sign of the Lovén rhythm in the electrical response, is reciprocal innervation completely abolished. But the suggestion has to be tested with some more suitable preparation, and if possible with two instruments arranged so as to record the electrical responses of two antagonistic muscles simultaneously.Incidentally it is shown that a reflex contraction depends for its strength on the duration of the central stimulus immediately producing it rather than on its strength, in so far as the electrical response of a muscle is a measure of the strength and duration of the immediate stimulus.Records on which statements made in earlier papers [(8) and (9); (7)] are based are here reproduced for the first time, showing (1) that when the possibility of secondary stimuli from the periphery affecting the cord is excluded, all the same types of response can be obtained as when no such precautions are taken, and that the duration of the response (when the cord is left in connection with the medulla oblongata) may be equally long; (2) that when the mechanical response of a muscle is relaxation, its electrical counterpart is (galvanometric) positivity.