142 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



If the muscle has been injured at B, the dying fibres there will react but 

 poorly to the stimulus, and therefore the antagonistic influence of the negative 

 change at B will incompletely compensate for the negativity at A, and hence 

 only a single phase due to the condition of negativity at A will be seen. 



The normally beating heart shows diphasic currents of action : in the first 

 phase the base, where the contraction process starts, is negative to the apex, 

 and in the second phase the apex is negative to the base. In case the heart be 

 injured, the negative change corresponding to action fails at the injured part, 

 and therefore a single and because not antagonized more prolonged negative 

 change is observed. Under certain conditions a triphasic change is observed, 

 which need not be discussed here. Waller l has succeeded in recording the 

 electrical changes which accompany the beat of the human heart. 



These diphasic changes of the electric condition are sufficiently strong and 

 rapid in the mammalian heart to excite the nerve of a nerve-muscle prepara- 

 tion, and the muscle will be seen to give one, or, if the heart is uninjured, 

 sometimes two, contractions every time the heart beats. 



Bernstein 2 found the time between the two portions of diphasic change to 

 be proportional to the distance between the leading-off electrodes, and to cor- 

 respond to a rate of transmission the same as that of the wave of excitation 

 as revealed by the spread of the contraction process (in the muscle of the frog 

 3 meters per second). Hermann, 3 by using cord electrodes on the human fore- 

 arm, found the rate of spread of the active process by the voluntary contraction 

 of human muscle to be from 10 to 13 meters per second. Du Bois-Reymond 

 dipped a finger of each hand into fluid contained in cups connected with a 

 galvanometer. If the muscles of one arm were vigorously contracted, a 

 deflection of the magnet was seen. This was probably due to electric currents 

 from the glands of the skin and not from the contracting muscles. Bernstein 

 found that the negative change began at the instant of excitation, i. e. during 

 what was considered the latent period, and hence he thought that it preceded the 

 contraction process and represented the excitation process. It is now believed 

 that the katabolic chemical changes which result in the development of the 

 three forms of energy, heat, motion, and electricity, have little or no latent 

 period, but begin at the instant the irritant acts, being practically synchronous 

 with the excitation process (see p. 101). The condition of negativity is con- 

 sidered not to result from an irritation process preceding the contraction, but 

 to be associated with the contraction process itself, and this view is supported 

 by the discovery that the negative state continues throughout the contraction. 

 Sanderson and Page 4 saw the diphasic change which accompanies the beat of 

 the heart last throughout the contraction. 



Lee 6 found the diphasic change which occurs when the skeletal muscle of 



1 Archiv filr Anatomic und Physiologic, 1890; physiol. Abtheil., p. 187. 



2 Untersuchungen uber den Erregungsvorgang im Nerven- und Muskel-systeme, 1871. 

 8 Handbuch der Physiologic, 1879, i. 1, p. 224. 



4 Journal of Physiology, 1879, vol. ii., p. 396. 



5 Archiv fur Anatomic und Physiologic, 1887, p. 204. 



