Physiology : A manual for students and practioners / by Theodore C. Guenther and Augustus E. Guenther.

  • Guenther, Theodore C. (Theodore Charles)
Date:
1903
Catalogue details

Licence: Public Domain Mark

Credit: Physiology : A manual for students and practioners / by Theodore C. Guenther and Augustus E. Guenther. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

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    inri'i'dsrs the iH'ijafirc ///vx-xj/rr in the clir.4. The mouths of the t/mit irin-f enij)tyinji; into the auricles are ititprorl^hd with culrcx, liiit are rich in circular mnnclr-jihn-x wliich, by their contraction, ni:iv obliterate the lumen of the vessels and so prevruf rrfjnnjita- lion. The systole of the heart is known to begin with tlie veins, and swee]> down over the auricles, and some have contended that the tlow of venous blood is never checked, but that the contracting vi'ins and auricles carry it snioollily into the ventricles by com- pensating l»y tiicir contraction for the expansion of the auricles and ventricles and the opening of the cuspid valves. The aai.^e of the rhijthiiiic movements of the heart lies within itself, since it can be severed from the central nervous system with- out necessarily destroying its activity. For some time many ob- servers contended that the rich nerve-supply was essential, but it has been shown that many forms of contractile substance may be rhythmically active. A strip of muscle cut from the apex of a tortoise's heart, which contains no ganglion-cells, and suspended in a moist chamber, may beat as long as thirty hours with a slow rhythm. Very small microscopical pieces from the bulbus aortas of the frog, which are proliably devoid of nerve-cells, contract rhythmically. Curarized striated muscle placed in certain saline solutions will show a regular rhythm for hours. Many inverte- brates have hearts that are not provided with nerve-cells. The Jirarf of fhr nnhn/o hrafs before the iierrex Jiare r/ro)r)) Into if. The canliac contraction is preceded by a change of electrical potential, which sweeps over it in the form of a wave. Both nor- mally take the same course, beginning at the great veins and spreading rapidly over the auricles, then a short pause, after which they spread over the ventricles. At times the contraction may originate in the ventricle. Thus, by drawing a tight liga- ture about the heart at tlie junction of the auricles and ventricles, the rhythm of the b.eart is disturbed and the ventricle beats with an independent slower rhythm. If the rJrctrienJ cha)i(/e.< of the beating heart are investigated, it is found that the base becomes negative before the apex, and that this condition of negative potential pas.«es along in the form of a wave to the apex. Its speed has been found to average at lea.'Jt 50 mm. a second. The /(iteiit jtrriod of frog's heart-muscle is about 0.08 of a second, but the change of potential takes place instantly after the applica- tion of the stimulus. The excitation wave can be made to paijS S—Phys.