Disembodied hearts and the limits of life
Then a dog's head, removed from the body but attached to an early heart and lung machine, is shown responding to simple stimuli. Finally, a dog is exsanguinated, attached to a heart and lung machine, and revived after ten minutes without a heartbeat.
Is it disturbing? Yes. But the basic technology and insights that scientists gained by reviving various organs created the possibility of organ transplantation, and the insight that the heart and lung machine could work made open heart surgery possible, and along with it, millions of lives extended.
Earlier work on these same lines was pioneered in the United States by John Gibbon, a doctor who was spurred to his research by the unfortunate death of a patient on an operating table. Beginning in 1930, he researched simple heart and lung machines, until, in 1953, he succeeded in bypassing a human heart, repairing a damaged atrial septum, and restarting the patient's heart. The history is nicely described in this article from the Journal of Cardiac Surgery, his 1953 patent is available online, and a good library probably has 1939's "The maintenance of life during experimental occlusion of the pulmonary artery followed by survival," (from Surg Gynecol Obstet) in which he describes experimental results from experiments in cats.
I've pointed out before that this era involved a major shift in society's understanding of life and death. In the film, the dog is declared dead when its heart stops, whereas we look at brain activity today. A major part of that shift was the advent of heart transplantation. A heart undergoes major changes after it stops beating, and experimental heart transplants worked best when the heart was removed before it stopped beating naturally. If death was defined in terms of the heart's activity, that meant the surgeon would be killing the patient by removing it. If death were defined in terms of brain activity, no moral or ethical concerns would apply.
The change in attitude wasn't instant, but work like what Drs. Gibbon and Bryukhonenko helped move us to a different view of where life ends. As we navigate the fraught waters of abortion, stem cells and other medical advances, it's worth bearing this mutability in mind.