1 00:00:06,379 --> 00:00:11,992 In 1881, doctor William Halsted rushed to help his sister Minnie, 2 00:00:11,992 --> 00:00:14,692 who was hemorrhaging after childbirth. 3 00:00:14,692 --> 00:00:17,501 He quickly inserted a needle into his arm, 4 00:00:17,501 --> 00:00:21,250 withdrew his own blood, and transferred it to her. 5 00:00:21,250 --> 00:00:25,105 After a few uncertain minutes, she began to recover. 6 00:00:25,105 --> 00:00:27,880 Halsted didn’t know how lucky they’d gotten. 7 00:00:27,880 --> 00:00:30,740 His transfusion only worked because he and his sister 8 00:00:30,740 --> 00:00:33,080 happened to have the same blood type— 9 00:00:33,080 --> 00:00:36,959 something that isn’t guaranteed, even among close relatives. 10 00:00:36,959 --> 00:00:39,890 Blood types hadn’t been discovered by Halsted’s time, 11 00:00:39,890 --> 00:00:43,760 though people had been experimenting with transfusions for centuries— 12 00:00:43,760 --> 00:00:46,160 mostly unsuccessfully. 13 00:00:46,160 --> 00:00:50,370 In 1667, a French physician named Jean-Baptiste Denis 14 00:00:50,370 --> 00:00:53,642 became the first to try the technique on a human. 15 00:00:53,642 --> 00:00:57,631 Denis transfused sheep’s blood into Antoine Mauroy, 16 00:00:57,631 --> 00:01:00,171 a man likely suffering from psychosis, 17 00:01:00,171 --> 00:01:02,971 in the hopes that it would reduce his symptoms. 18 00:01:02,971 --> 00:01:05,711 Afterward, Mauroy was in good spirits. 19 00:01:05,711 --> 00:01:08,969 But after a second transfusion, he developed a fever, 20 00:01:08,969 --> 00:01:13,171 severe pain in his lower back, intense burning in his arm, 21 00:01:13,171 --> 00:01:17,101 and he urinated a thick, black liquid. 22 00:01:17,101 --> 00:01:19,071 Though nobody knew it at the time, 23 00:01:19,071 --> 00:01:24,811 these were the signs of a dangerous immune response unfolding inside his body. 24 00:01:24,811 --> 00:01:28,171 This immune response starts  with the production of proteins 25 00:01:28,171 --> 00:01:29,500 called antibodies, 26 00:01:29,500 --> 00:01:33,181 which distinguish the body’s own cells from intruders. 27 00:01:33,181 --> 00:01:37,601 They do so by recognizing the foreign proteins, or antigens, 28 00:01:37,601 --> 00:01:40,484 embedded in an intruder’s cell membrane. 29 00:01:40,484 --> 00:01:42,799 Antibodies latch onto the antigens, 30 00:01:42,799 --> 00:01:47,452 signaling other immune cells to attack and destroy the foreign cells. 31 00:01:47,452 --> 00:01:50,952 The destroyed cells are flushed from the body in urine. 32 00:01:50,952 --> 00:01:54,321 In extreme cases, the massive break down of cells 33 00:01:54,321 --> 00:01:59,196 causes clots in the bloodstream that disrupt the flow of blood to vital organs, 34 00:01:59,196 --> 00:02:02,946 overload the kidneys, and cause organ failure. 35 00:02:02,946 --> 00:02:06,421 Fortunately, Denis’s patient survived the transfusion. 36 00:02:06,421 --> 00:02:10,221 But, after other cross-species transfusions proved fatal, 37 00:02:10,221 --> 00:02:13,134 the procedure was outlawed across Europe, 38 00:02:13,134 --> 00:02:16,274 falling out of favor for several centuries. 39 00:02:16,274 --> 00:02:21,066 It wasn’t until 1901 that Austrian physician Karl Landsteiner 40 00:02:21,066 --> 00:02:22,766 discovered blood types, 41 00:02:22,766 --> 00:02:27,786 the crucial step in the success of human to human blood transfusions. 42 00:02:27,786 --> 00:02:32,463 He noticed that when different types were mixed together, they formed clots. 43 00:02:32,463 --> 00:02:36,543 This happens when antibodies latch on to cells with foreign antigens, 44 00:02:36,543 --> 00:02:38,967 causing blood cells to clump together. 45 00:02:38,967 --> 00:02:43,284 But if the donor cells are the same blood type as the recipient’s cells, 46 00:02:43,284 --> 00:02:48,363 the donor cells won’t be flagged for destruction, and won’t form clumps. 47 00:02:48,363 --> 00:02:49,713 By 1907, 48 00:02:49,713 --> 00:02:54,476 doctors were mixing together small amounts of blood before transfusing it. 49 00:02:54,476 --> 00:02:56,996 If there were no clumps, the types were a match. 50 00:02:56,996 --> 00:02:59,728 This enabled them to save thousands of lives, 51 00:02:59,728 --> 00:03:03,528 laying the foundation for modern transfusions. 52 00:03:03,528 --> 00:03:07,368 Up to this point, all transfusions had occurred in real time, 53 00:03:07,368 --> 00:03:10,194 directly between two individuals. 54 00:03:10,194 --> 00:03:13,428 That’s because blood begins to clot almost immediately 55 00:03:13,428 --> 00:03:15,588 after coming into contact with air— 56 00:03:15,588 --> 00:03:20,388 a defense mechanism to prevent excessive blood loss after injury. 57 00:03:20,388 --> 00:03:25,078 In 1914, researchers discovered that the chemical sodium citrate 58 00:03:25,078 --> 00:03:31,092 stopped blood coagulating by removing the calcium necessary for clot formation. 59 00:03:31,092 --> 00:03:34,532 Citrated blood could be stored for later use— 60 00:03:34,532 --> 00:03:39,484 the first step in making large scale blood transfusions possible. 61 00:03:39,484 --> 00:03:46,472 In 1916, a pair of American scientists found an even more effective anticoagulant 62 00:03:46,472 --> 00:03:51,791 called heparin, which works by deactivating enzymes that enable clotting. 63 00:03:51,791 --> 00:03:54,331 We still use heparin today. 64 00:03:54,331 --> 00:03:55,422 At the same time, 65 00:03:55,422 --> 00:03:59,342 American and British researchers developed portable machines 66 00:03:59,342 --> 00:04:04,584 that could transport donor blood onto the battlefields of World War I. 67 00:04:04,584 --> 00:04:07,034 Combined with the newly-discovered heparin, 68 00:04:07,034 --> 00:04:10,825 medics safely stored and preserved liters of blood, 69 00:04:10,825 --> 00:04:15,817 wheeling it directly onto the battlefield to transfuse wounded soldiers. 70 00:04:15,817 --> 00:04:20,523 After the war, this crude portable box would become the inspiration 71 00:04:20,523 --> 00:04:25,436 for the modern-day blood bank, a fixture of hospitals around the world.