. Elements of human physiology. Physiology. NERVE-FIBRES (CONDUCTING TISSUES) 171 The results of stimulating motor nerves by means of constant currents were stuclied by Pfliiger and, embodied in a table, make up what is known as Pfliiger's law. The result of stimulation varies with the strength of a current. Laiv of Contracticm Strenglib of current. Ascending. Descending. Make. Break. Make. Break. Weak .... 0 0 0 Medium c c C c Strong 0 C or T C or T 0 c = contraction. C = strong contraction. T = tetanus. 0 = no effect. With the weakest currents, excitation occurs only at make, since a make- s
. Elements of human physiology. Physiology. NERVE-FIBRES (CONDUCTING TISSUES) 171 The results of stimulating motor nerves by means of constant currents were stuclied by Pfliiger and, embodied in a table, make up what is known as Pfliiger's law. The result of stimulation varies with the strength of a current. Laiv of Contracticm Strenglib of current. Ascending. Descending. Make. Break. Make. Break. Weak .... 0 0 0 Medium c c C c Strong 0 C or T C or T 0 c = contraction. C = strong contraction. T = tetanus. 0 = no effect. With the weakest currents, excitation occurs only at make, since a make- stimulus, the rise of katelectrotonus, is always more effectual than a break- stimulus, the disappearance of anelectrotonus. With currents of moderate strength, excitation occurs both at make and break, being better marked at make, especially in the case of descending currents. With very strong currents, we get a contraction at make only when the current is descending, since, when Fig. Arrangement of experiment to demonstrate Pfliiger's law of contraction. the current is ascending, the excitation started at the kathode cannot pass the block at the anode. For the same reason a break contraction is obtained only with an ascending current, since at the break of a descending current there is a swing-back of the nerve at the kathode to a condition of diminished irritability, which effectually blocks the excitation started higher up the nerve at the anode. The aiTangement of the experiment for demonstrating Pfliiger's law is shown in Fig. 80. The strength of the current is graduated by means of the rheochord, the current being led into the nerve by means of non-polarisable electrodes. It is extremely important in these experiments to avoid any injury or drying of the nerves at either of the two electrodes, since the excita- tory efi'ect either at make or break would be abolished by local Please note that these images are extracted from scanned page images that
Size: 2141px × 1167px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectphysiology, bookyear1
