PRESIDENT’S ADDRESS. 417 
still left in the incompletely oxidised bodies excreted in the urine 
(urea) must be deducted from the amount originally present in the 
food. Further, air must be passed through the calorimeter for the 
animal to breathe. This becomes heated and saturated by mois- 
ture, and the amount of heat so lost must be determined. 
Within the last few years Rubner has succeeded in overcoming 
all the experimental difficulties, and has obtained remarkably 
accurate results, which leave no doubt that the laws of conservation 
of energy apply equally well for animals as for much simpler 
mechanisms. The satisfactory determination of this point is of 
far-reaching importance. If the processes going on in an animal 
are regulated by such a fundamental law of physics, it is hard to 
conceive that the details of such processes, however impossible of 
interpretation by present knowledge of chemistry or physics, can 
be of an entirely different nature. 
Of all progress during the last half-century, perhaps the most 
striking has been the increase in our knowledge concerning the 
nervous system. We are now able to locate with some accuracy 
the anatomical situations in the central nervous system, the 
integrity of which is essential to the performance of a particular 
function. We know, for instance, that in the higher animals certain 
superficial cerebral areas (the cortical areas) are fundamentally 
concerned with definite muscular acts of the opposite side of the 
body. Stimulation of such situations calls forth the corresponding 
movement, whereas destruction of these spots gives rise to paralysis, 
more or less lasting, of the voluntary expression of this movement. 
Nor is this all; careful examination of monkeys waich have had 
the so called cortical motor centres removed, shows that as well as 
definite paralysis of some of the movements of the opposite side of 
the body, they exhibit distinct blunting of sensation over the same 
area. 
Other parts of the cerebral cortex have been found in the same 
way to be associated with the special senses, and the effects of 
disease in man have shown that a similar differentiation of nervous 
paths exists. The result of this kind of work, as well as possess- 
ing all the extraordinary interest attached to any discoveries con- 
cerning the nervous system, has been fruitful in providing facts 
which have been of immediate service in the domain of practical 
medicine. 
Advance in knowledge of the nervous system has, however, been 
mainly anatomical. Much of what seemed an entangled mass of 
nerve-cells and their processes—nerve-fibres—of so great com- 
plexity as to baffle all attempts at unravelling, has slowly unfolded 
its scheme, after arduous research by new methods. 
By the methods of anatomical research introduced by Waller 
and Flechsig, the arrangementof the nerve-fibresinto definite tracts, 
and the origin and distribution of these tracts has been discovered, 
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