From time to time popular and scientific attention has been centered upon the intelligence of horses. Among the various trick horses exhibited for entertainment, there have been some outstanding examples. Der kluge Hans ( 5) is perhaps the most famous member of this group. About the year 1900 a retired Prussian schoolmaster, Herr von Osten, began to train a fiveyear-old stallion of Orloff trotting stock for four years according to the same methods used with children. The horse was free, and wholly managed by voice and frequent rewards of bread and carrots. The achievements of Hans were remarkable. He could answer number problems in the four fundamental processes, spell out answers to questions according to the system von Osten used, and furthermore showed some appreciation of harmony in music. His patient teacher believed Hans really understood the painstaking lessons.Cav. Emilio Rendich, an Italian painter in Berlin, was the first to note the fact that the horse was guided by minute movements of the trainer which were, however, wholly unconscious on his part. These signals were later, demonstrated with considerable thoroughness by Dr. Oskar Pfungst (2), much to the confusion of von Osten.In 1905 Herr Karl Krall, a wealthy jeweler of Elberfeld, prevailed upon the disappointed old schoolmaster to permit his participation in the training of Hans. Krall also purchased and trained two Arabian stallions, Muhammed and Zariff, who soon surpassed Hans. Various improvements in technique furthered