On the physiology of the embryonic heart : being a thesis for the degree of Doctor of Science of the Universty [i.e. University] of London, 1893 / by J.W. Pickering.

  • Pickering, John William.
Date:
1893
Catalogue details

Licence: Public Domain Mark

Credit: On the physiology of the embryonic heart : being a thesis for the degree of Doctor of Science of the Universty [i.e. University] of London, 1893 / by J.W. Pickering. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    1. Temperature. Bach embryo has an individual rhythm of its own, which, if the conditions arc constant, remains unaltered, but different embryos, even of the same age, may have different rhythms, so that it is neces- sary to detennine for each embryo its normal rhythm before varia- tions can be studied. An embryo’s heart, aged seventy-two hours, at a temperature of 31° C., was beating with a regular rhythm of 84 per minute. The temperature of the air of the chamber was rapidly raised to 42° C., when the rhythm rose to 91 per minute. A further rise to 50° C. increased the idiythm to 128, it still remaining regular. The temperature was then rapidly lowered to 26° C., when the rhythm fell to 114 per minute. A further fall to 16° C. reduced the rhythm to 34 per minute. The temperature was then raised to 46° C., when the rhythm rose to 117° per minute. On again letting the tempera- ture fall to 26° C., the rhythm fell to 36° per minute. The above experiment, taken as an instance fi’om several, sliows that, other factors being constant, the rhythm of the embryonic heart varies directly with the temperature of the surrounding medium. Extremes of temperature stop the heart; thus exposure to a tem- perature of 10° C. causes the beats to become weaker and slower, and finally to stop in diastole. If the air of the incubator be raised above 50° 0., the beats become so rapid as to be uncountable. They are feeble, and the heart is pale, due to the passage of less blood through it than in the normal state. Violent systolic spasms alternate with periods of quiescence. It stops in an expanded condition when the surrounding temperature is about 55° C. Lowering the tem- perature restores the beating, but the heart is enfeebled. If the temperature is raised much above this limit the heart is killed. Mechanical stimulation of the heart in standstill, due to either extreme of temperature, if applied at the ventricular end, gives rise to one or more waves of contraction, commencing from the auricular end, and showing the direct conduction through the fibres of the heart. The heart will respond to aui’icular stimulation when irre- sponsive to ventricular stimulation. Small variations of temperature, such as one or two degrees, occurring over a long period of time, as in an hour, do not affect the rhythm. 2. The Introduction of Drugs. The drugs employed were applied directly to the heai’t substance at the temperature of the embryo, and dissolved in noi-mal saline (0'65 per cent, sodium chloride) solution. a. Caffeine.—An embryo, aged sixty-eight hours, at 33° C. had a rhythm of 88 per minute. To its heart O’OOOIS gi'am* of caffeine was * All weights of drugs used are eijjressed in gmms.