The prolonged researches of over twelve years of Professor Pawlow and his colleagues on dogs afford a body of evidence as to the possibility of producing new reflexes in the life of an individual which have never been questioned. In 1913 at Groningen, before the International Congress of Physiologists, he gave a brief account of this work. His previous work on the digestive glands carried on by delicate operations in which the œsophagus was diverted from the stomach and made to open externally, and in which a portion of the stomach was diverted from the rest and a new “small stomach” was formed, gave him the opportunity of immensely important insight into the factors governing the work of the various glands of the stomach. The work of others showed similar results in the pancreas. I only refer to these because they lead up to the special artificial results with new reflexes which he described in 1913. He states that the nervous system besides the primitive function of reproducing innate reflexes, possesses another prime function-namely the formation of new reflexes; and that the living thing is enabled to respond, by definite and suitable activities to agencies to which it was formerly indifferent. His experiments on the formation of “conditional reflexes,” as he calls them rather than “acquired” as opposed to “innate,” are grouped around the feeding of the animal and mainly deal with the salivary glands, because they are in direct connection with the external world and their reactions are simply and easily observed. An indifferent stimulus is chosen for the reflexes which it is desired to build up, and this is applied at the same time as food or acid is introduced in the mouth. After a few sittings it is found that this indifferent stimulus _alone_ is now capable of calling forth a secretion of saliva. “The conditional reflex has been formed; the formerly indifferent stimulus has now found a path to the requisite part of the central nervous system. The reflex-arc has now a different afferent neurone.” He gives a good example of this in the result of the application of painful stimuli by a strong electrical current to the skin, systematically accompanying each feeding of the animal. He finds that the strongest electrical stimuli applied to the skin give rise merely to the “feeding reaction,” that is, the secretion of saliva, and no indications of any fright or pain appear. “The skin of a dog can be subjected to cutting, pinching or burning, and the only result we shall obtain will be the manifestation of what, judging from our own experience, we should call the symptoms of the keenest appetite; the animal follows the experimenter about, licks himself, and saliva flows in abundance.” This, it must be remembered, occurs in the absence of the offer or sight of food, _at the time in question_. He adds: “In this way we have been able to divert the impulses from one path to another according to the conditions, and we cannot avoid