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D.—ZOOLOGY 85 
be independent of his epoch, and Descartes was in some respects a direct 
heir of the Middle Ages ; he shared their preoccupation with reason and 
the soul of man. He was primarily a mathematician and a theologian ; 
he had unlimited faith in the power of the human intellect; he was 
concerned to demonstrate the existence of God, and to uphold the belief 
that man’s soul is immortal, that he is not as the beasts that perish. At 
the same time, he was profoundly influenced by the physical and cosmo- 
logical conceptions introduced by Copernicus and Galileo, and grasped 
their enormous significance. He was acquainted with the work of his 
great contemporary, William Harvey, on the circulation of the blood, and 
made great play in his books with a somewhat crude attempt to explain 
all physiological processes mechanically. It was he who imposed 
dualistic materialism upon biology as its working method. 
Although nowadays modern physics has completely transformed the 
old conception of matter, and has little use for the notion of material 
determinism, it is not so long ago that materialism was the orthodox creed 
of science, and we are in biology still suffering from the after-effects. 
I do not think I can better describe the fundamental tenets of this creed 
than by quoting a passage from T. H. Huxley’s essay on The Progress 
of Science, which appeared in 1887. ‘ All physical science,’ he wrote, 
“starts from certain postulates. One of them is the objective existence 
of a material world. It is assumed that the phenomena which are com- 
prehended under this name have a “ substratum ” of extended, impene- 
trable, mobile substance, which exhibits the quality known as inertia, 
and is termed matter. Another postulate is the universality of the law 
of causation ; that nothing happens without a cause (that is, a necessary 
precedent condition), and that the state of the physical universe, at any 
given moment, is the consequence of its state at any preceding moment. 
Another is that any of the rules, or so-called “‘ laws of Nature,” by which 
the relation of phenomena is truly defined, is true for all time. The 
validity of these postulates is a problem of metaphysics ; they are neither 
self-evident nor are they, strictly speaking, demonstrable.’ 1 
As a counterpart to this abstract concept of matter as extended substance 
we have the concept of mind as inextended thought. Physical science, 
and here I include physiology, has never known quite what to do with 
mind. In practice it has ignored mind, and treated it as an ‘ epipheno- 
menon’ accompanying, but not influencing, certain physiological pro- 
cesses taking place in the central nervous system.2 For the practical 
purpose of research it has treated the animal as a mechanism, and sought 
to analyse its working in detail. This theory, that the animal is to be 
regarded, from the point of view of science, as a physiological automaton, 
we find explicitly stated by Descartes nearly 300 years ago in his Discours 
1 Method and Results, London, 1893, pp. 60-61. : 
? Cf. Huxley: ‘ The consciousness of brutes would appear to be related to the 
mechanism of their body simply as a collateral product of its working, and to be 
as completely without any power of modifying that working as the steam- 
whistle which accompanies the work of a locomotive engine is without influence 
upon its machinery.’ Ibid., p. 240. 
