METHODS OP PHYSIOLOGICAL RESEARCH 13 



spirits, and happily thought to put in its place heat as the cause 

 of vital phenomena, emphasized the fact that the nutrition of the 

 whole body is provided for by the blood alone. By these special 

 investigations into the physiology of the blood, the path was made 

 easy to the greatest discovery of this period, that of the circulation 

 of the blood by Harvey (1578-1657). The importance of Harvey's 

 discovery lies in the fact that he first established the physiological 

 connection of the arteries and veins peripherally, and the passage 

 of the blood from the arteries into the venous trunks and thence 

 to the heart ; he thus laid a basis for the fact that all the blood 

 passes through the heart and moves in a closed circuit through 

 the whole body. He added to this a great number of special facts 

 concerning the mechanism of the circulation, all of which — and 

 herein lies the great significance of his work — rested upon keen 

 observation and an exact experimental basis. Following the exact 

 tendencies of his time — the time which brought forth also a. 

 Copernicus, a Galileo, a Bacon, and a Descartes — Harvey, by his 

 brilliant discovery, raised the experimental method again to an 

 honourable position in physiology, after it had remained in complete 

 oblivion for thirteen centuries. The spirit of the conscientious 

 investigator and great logical acuteness characterise Harvey's 

 personality and stamp him as the first real physiologist after the 

 long night of the middle ages. A second doctrine " de generatione 

 animalium," stands with equal honour by the side of his doctrine 

 of the circulation of the blood. In this he put forward the dictum, 

 " omne vivum ex ovo," which has since obtained vast significance in 

 the science of life, and in the various forms in which it has been ex- 

 pressed in recent times controls all modern physiological views of 

 organic reproduction. 



Of the adherents of the great theosophical school which Para- 

 celsus instituted, one only is important in the history of physiology, 

 namely, van Helmont (1577-1644), since, in spite of the mysticism 

 that characterised the whole theosophical tendency, he made 

 thoroughly accurate observations. Starting with the Paracelsian 

 doctrine of the unity and the constant development of nature, he 

 conceived all natural bodies to be composed of matter and " archeus " 

 (energy). Things exist and live only in this combination. As a 

 result of it, all things are living. There are, however, different 

 grades of life, and the so-called lifeless bodies exist at the lowest 

 grade. Among van Helmont's special physiological ideas, his 

 chemical doctrine of ferments is especially interesting. He rejects 

 Galen's idea that digestion goes on in the stomach through the 

 action of heat, and puts in its place the correct conception, that 

 digestion is performed hy a " ferment " associated with the gastric 

 juice. 



The philosophical systems of Francis Bacon (1561-1626) and 

 Descartes (1596-1650) exercised a great influence upon the further 



