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must pass to the researches of an Englishman — the immortal Harvey. 
With the discovery of the circulation of the blood by Harvey, the 
death blow was given to the doctrine of the spirits. Harvey’s ex- 
planation of the blood flow was essentially mechanical, and this view 
of the famous physician of Charles I. opened up a path which was 
followed with brilliant success by succeeding physiologists. 
Whilst Harvey was making his investigations on the living 
organism, the science of physics was ’progressing rapidly. Galileo 
had been made Professor of Physics at Padua just six years before 
Harvey had reached that place, and epoch-making discoveries had 
been made in a new school of exact science. About the same time, 
four years after Galileo reached Padua to be exact, and in the year 
159(3, there was born near Tours in France the man whom we may 
consider as the real father of the mechanistic conception of the 
organism. I refer to Rene Descartes. He was a great mathe- 
matician, but neither a physiologist nor anatomist. He studied both 
subjects, however, as an amateur and even wrote a popular treatise 
which might be called the first text book of physiology. The point 
to be emphasised here is that lie wrote to sIioav that the new vieAvs 
and laws of physics might be applied to the living organism, and 
that the human body might also be looked on as a machine. Never- 
theless, Descartes found it necessary to add an additional factor to 
his machine which he called the “Rational Soul.” The Soul was sup- 
posed to be concerned in all thought, intelligence, memory, sensation 
and imagination, it was apparently not at all necessary for the 
ordinary functions of the body. 
We must pass very quickly over further historical details, but 
I must draw your attention to the growth of another school which 
introduced the knowledge of the chemists and combined the forces of 
physics and chemistry in an endeavour to explain the phenomena 
of life. At this period, however, the physicists and chemists were not 
able to do very much after all, and the unexplainable became the 
support of a theory of Vital Force which now for the first time 
burst forth in definite form. The theory of Vital Force was put 
forward by the followers of Haller (1708-1777). This force was 
supposed to control and be responsible for all physiological pro- 
cesses whilst chemical and physical forces were confined to the phe- 
nomena of non-living matter. The result Avas disastrous. The phrase 
Vital Force became sufficient, became in fact the actual explanation 
(a lazy and stifling explanation) of all difficult problems in physio- 
logy. 
The last period to be referred to leads on to to-day. It coincides 
with the victories of physiological chemistry and may be said to 
have commenced with the synthesis of Urea, an organic compound 
formed only by organisms. This Avas achieved by Wohler in 1828, 
and the discovery greatly stimulated the che.mical explanation of 
life phenomena. From this date physiologists have applied 
