6o8 THE POPULAR SCIENCE MONTHLY 



sion of knowledge and interest (which was in the main a consequence 

 of the new insight), bnt by the introduction of a new interpretation. 

 Familiar facts were given a distinctive and a richer meaning. The 

 perspective of significance was notably altered. This momentous re- 

 construction of the biological realm indicates in a few words the de- 

 cisive factors that made modern psychology possible. The brevity of 

 the record should not diminish the appreciation of its vital importance. 

 The development of the knowledge of nervous function has a ven- 

 erable history. The recognition of sensation and movement in relation 

 to the nerves occurs sporadically and irregularly in Greek, Eoman and 

 medieval medicine, at times with a shrewd interpretation of symptoms. 

 It seems never to have been made a leading principle, but was held 

 in detachment from the general notions in terms of which conclusions 

 were stated. Hippocrates, Galen and their followers occasionally re- 

 cord observations in which a limited loss of movement (paralysis) and 

 loss of sensation (anesthesia) were referred to interference with the 

 action of certain nerve-trunks. Such observations remained casual 

 and incidental. The usual explanation of the bodily accompaniments 

 of mental action were given in terms of the flow of the " vital " spirits, 

 with the veins (supposed to contain air) as the true channels of the 

 flow that determined sensation; while the ventricles (literally breath- 

 ing spaces — actually the channels for the oerebro-spinal fluid) were 

 assigned the central part in the vital service. Vesalius, founder of 

 modern anatomy, knew by experiment apparently as well as through 

 inference from observation, that section of the nerves abolished mus- 

 cular control and that the loss of the medulla deprived an animal of 

 sensation and movement. He contested the notion that faculties like 

 memory could reside in such spaces as the ventricles of the brain. But 

 such views were heretical to the scriptural authority of Galen and 

 Hippocrates, and were timidly expressed and pursued. As a type of 

 conception matured under philosophical pursuits critically maintained 

 and in relation to the science of the day, may be cited the view of 

 Descartes. He looked upon the nervous system as a mechanical autom- 

 aton — somewhat after the manner of an elaborate and fantastic 

 "playing" fountain, whose ingenious streams turned windmills and 

 started miniature water-spouts. The nerves were conceived as tubes 

 for the flow of "animal spirits," or of some similar agency, with the 

 pineal gland in the center of the system as a controlling valve directing 

 the flow — the flow according to the course resulting in one kind or an- 

 other of mental process. Even Willis, despite his insight into the 

 structure and function of the brain and the complex provisions for its 

 circulatory system, could speak of it as an instrument which the " soul 

 inhabits and adorns with its presence." He conceived the blood as a 

 vital flame, through which products of combustion arose and in turn 

 gave rise to mental processes. Each variety of physical change which 



