152 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



are to be observed on the normal muscle. To understand this we must con- 

 sider the diphasic current of action. 



Diphasic Owrr&rd of Actum. — If a normal muscle be locally stimulated by 

 a single irritation, either directly or indirectly through its nerve, the part 

 excited will be the first to become active and electrically negative, and this 

 condition will be taken on later by other parts. Our methods only permit us 

 to observe the relative condition of the parts of the muscle to which the elec- 

 trodes are applied, the changes in the intermediate tissue failing to show theru- 

 selves. If an electrode be applied near the place where the uninjured 

 muscle is stimulated. .1, and another at some distant point, B, and these 

 electrodes be connected with a capillary electrometer, a diphasic electrical 

 change will be observed to follow each stimulation. At the instant the irritant 

 is applied the muscle-substance at A will become suddenly negative with 

 respect to that at B ; when the spreading irritation wave has reached B, that 

 part too will tend to be negative, and an electrical equality will be temporarily 

 established; finally, B continuing to be active after A has ceased to act, B 

 will be negative in respect to A. Since the wave of excitation spreads along 

 the fibres in both directions from the point irritated, each excitation will cause 

 diphasic electrical changes to either side of the place to which the irritant is 

 applied. 



lt^ 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 >ingle phase due to the condition of negativity at A will be seen. 



The normally beating heart ventricle shows diphasic currents of action : 

 in the first phase the base, where the contraction process start.-, is negative to 

 the apex, and in the second phase the apex is negative to the base. In ease 

 the heart be injured, the negative change corresponding to action fails at the 

 injured part, and therefore a single and because not antagonized more pro- 

 longed negative change is observed. Under certain conditions a triphasic 

 change is observed, which need not be discussed here. Waller 1 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 lie seen to give one, or, if the heart is uninjured, 

 sometimes two, contractions avevy 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- 



1 Archiv fur Anatomu und Physiologie, 1890; physiol. Abtheil., S. 187. 



2 Untersuch a 1,,/,-n iiber den Erregungsvorgang im Nerven- mul Mu.<kel-system, 1871. 



3 Bandbuch der Physiologie, 1879, i. 1, S. 224. 



