342 PSYCHOTHERAPY : SCIENTIFIC AND RELIGIOUS chap.
able definitely to trace objectively the gradual passage from the hypnotic trance into true sleep. This wholly natural transition accounts very simply and logically for the so-called lethargic state of hypnosis, which has often been observed and contrasted with the so-called alert stage. Thus the extreme lethargic state is not hypnosis, but true sleep ; only the alert stage is hypnotic.
Bass' experiment has been repeated at the Institute of Experimental Psychology at Oxford. The hypnotized subject is placed in an armchair raised about twenty inches from the ground. One leg (so far it has always been the right leg) is supported on a stool while the other is left in such a position that it can swing backwards and forwards with ease in order to facilitate the action of the reflex. An apparatus is mounted on an adjustable platform at the back in such a way as automatically to deliver a blow of the hammer against the patellar tendon every ten seconds. The action of the hammer is controlled by a large cam which, in turn, is driven by a constant speed motor regulated by a carefully constructed system of gears. The cam is so arranged that it catches the hammer at its first rebound from the blow and at once withdraws it for the next blow. The automatic recording of the knee jerk is accomplished by means of a stout line which extends from the heel of the subject's shoe to a vertical lever which marks a sheet of smoked paper. Around the subject's chest is placed the tube-like Sumner pneumograph, which communicates by means of a tube with a tambour provided with a recording pen for tracing the respiration. Many subjects have submitted to tests by this apparatus and have responded in a satisfactory way.
Moreover, while in normal sleep the subject is unable to perform simple voluntary acts which have been