The experience of a small-town German doctor would, in the mid-1870s, starta formidable transfusion craze. Oscar Hasse of Nordhausen am Harz triedtransfusion with lamb blood on fifteen patients, reported positive results inmeetings and publications, and suddenly hundreds of lamb blood transfu-sions were made in clinics, hospitals and lunatic asylums across Europe andthe USA. ‘The blood of lamb and sheep was flowing in streams, the literatureon transfusion was growing like an avalanche from day to day’, a contempo-rary observer noted.1Doctors used it as a cure for phthisis, pellagra, cancerand epilepsy,suggested it as a means to reawaken seemingly dead soldiers onthe battlefield. It was seen as ‘life-giving, despite its repulsive animality’.2I first encountered this phenomenon when researching for a book on thehistory of Swedish blood transfusions. I found that several lamb blood trans-fusions had been made in Sweden in the 1870s.3It turned out that they werepart of a wider international story. Lamb blood transfusion appeared in theearly 1870s, caught on and multiplied, then disappeared. This piqued my cu-riosity. Why this sudden fervour for transfusing strange blood? How was itundertaken, by whom, and how did the patients feel? And, most importantly: Did it work?