An introduction to physiology / by Augustus D. Waller.

  • Augustus Desiré Waller
Date:
1893
Catalogue details

Licence: Public Domain Mark

Credit: An introduction to physiology / by Augustus D. Waller. Source: Wellcome Collection.

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    all parts is at its maximum in the sinus, at its minimum in the ventricle, while in the ventricle it is greater at the base than at the apex ; contraction normally starts from the point of greatest instability, i.e. from the sinus ; removal of the sinus removes a leading part and causes shock, and the beat of the rest of the heart ceases for a period; after a time the beat recommences,, contraction starting from the auricle ; a second Hgature or section removing the auricle may cause a similar result, viz. a tempo- rary cessation of the ventricular beat, or if (omitting the ligature at the sinus-auricle junction) a ligature be at once applied to the auriculo-ventricular groove, the ventricle will be temporarily arrested in diastole. In short, though usually the first ligature gives arrest which is ended by the second Hgature, yet under varied conditions the first Hgature may fail to give arrest, or the second Hgature may give arrest. The results are thus not only complex, but variable, and cannot be made to bear any precise significance. No corresponding results have been obtained on the mammalian heart; if ah nervous communication between the auricles and ventricles be destroyed, the chambers continue to beat, but with independent rhythms; vagus stimulation now fails to arrest the ventricles, while it stiH produces auricular standstill. * All or nothing.'—But if the theoretical significance of Stan- nius' experiments is obscure or doubtful, it is otherwise as regards- their practical value. The first Stannius ligature affords a con- stantly employed means of obtaining the frog's heart in a quies- cent state, when it can be excited and employed for experiments, which cannot be made while it is spontaneously beating. ^ If a ' Stanniused ' and consequently quiescent frog's heart be subjected to stimuH of gradually increasing strength, it is found that the weakest stimulus which produces any effect at aU, produces all the effect of which the muscle is capable, in other words the effect is at once a maximum effect; a single stimulus either produces no effect at ah, or it produces the fuU effect of which the muscle is capable; ' all or nothing ' is the motto of the heart's contraction under these circumstances. To what extent may we suppose that this holds good for the normal beat ? Do a succession of normal systola vary in strength, or are they uniform and maximal ? The usual answer is that they are normally maximal and com- plete, and that the ventricle normally empties itself of its contents completely, but it is obvious that this does not imply equality in successive contractions, for the successive charges vary in
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