File:American journal of physiology (1898) (14595676599).jpg

Identifier: americanjourn01ameruoft (find matches)
Title: American journal of physiology
Year: 1898 (1890s)
Authors: American Physiological Society (1887- ) American Physiological Society (1887- ). Abstracts of papers presented at the fall meeting American Physiological Society (1887- ). Proceedings
Subjects: Physiology Physiology
Publisher: (Bethesda, Md., etc.) American Physiological Society (etc.)
Contributing Library: Gerstein - University of Toronto
Digitizing Sponsor: University of Toronto

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egree of lessening in the forceof the sinus contraction down to this stage, in which the recordtrembles on the verge of complete obscurity. The arrest of the heartin these experiments is therefore only apparent. The excitation isstill rhythmically discharged, but the resistance to its overflow uponthe sinus, auricle, and ventricle is so much increased under the influ-ence of the vagus that the change in form ceases to be measurable inthe auricle and ventricle and is barely measurable in the sinus. Evi-dently should the conduction become still more difficult, even thesinus contraction would cease to be measurable, although contractionmight still take place. The change in rhythm just discussed is only apparent; the truerhythm of the heart, nameh-, the frequency with which the excitationv.ave is discharged in the sinus, has been unaltered. But we have todeal also with changes in the true rhythm. It has already been shownthat the true rhythm may be increased or diminished by vagus action.
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Figure ii. Three-fifths the original size. The ventricle was suspended in such a waythat the contractions of the sinus, auricle, and ventricle are written in one curve. Theblack band in the line below marks the duration of the vagus excitation. The timeis in tenths of seconds. An additional example may be cited. In a R. catesbeiana the move-ments of the auricle and ventricle were recorded in one curve and themovements of the sinus in another. On excitation of the vagus theauricle and ventricle ceased to record, while the sinus beat with in-creased frequency. These cases can be readily explained by changesin the conducting power.^ The number of excitation waves dis-charged from the sinus must depend largely on the resistance to thedischarge. If the resistance is great, the threshold value will be high,and the discharge relatively infrequent; if the resistance is slight, thethreshold value will be low and the discharge relatively frequent. ^ Compare Exgelmaxn : Archiv f. d. ges. Physiol

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