10 REPORT—1899. 
as chemical, while some are, apparently at least, none of these. In the 
seventeenth century William Harvey, laying hold of the central mechanism 
of the blood stream, opened up a path of inquiry which his own age and 
the century which followed trod with marked success. The knowledge of the 
mechanics of the animal and of the plant advanced apace ; but the physical 
and chemical problems had yet to wait. The eighteenth century, it is 
true, had its physics and its chemistry ; but, in relation at least to the 
problems of the living being, a chemistry which knew not oxygen and a 
physics which knew not the electricity of chemical action were of little 
avail. The philosopher of 1799, when he discussed the functions of the 
animal or of the plant involving chemical changes, was fain for the most 
part, as were his predecessors in the century before, to have recourse to 
such vague terms as ‘ fermentation’ and the like ; to-day our treatises on 
physiology are largely made up of precise and exact expositions of the 
play of physical agencies and chemical bodies in the living organism, He 
made use of the words ‘vital force’ or ‘vital principle’ not as an occasional, 
but as a common, explanation of the phenomena of the living body. During 
the present century, especially during its latter half, the idea embodied 
in those words has been driven away from one seat after another ; if we 
use it now when we are dealing with the chemical and physical events of 
life we use it with reluctance, as a dews ex machina to be appealed to 
only when everything else has failed. 
Some of the problems—and those, perhaps, the chief problems—of the 
living body have to be solved neither by physical nor by chemical methods, 
but by methods of their own. Such are the problems of the nervous 
system. In respect to these the men of 1799 were on the threshold of 
a pregnant discovery. During the latter part of the present century, 
and especially during its last quarter, the analysis of the mysterious 
processes in the nervous system, which issue as feeling, thought, 
and power to move, has been pushed forward with a success conspicuous 
in its practical, and full of promise in its theoretical, gains. That 
analysis may be briefly described as a following up of threads. We 
now know that what takes place along a tiny thread which we call a 
nerve-fibre differs from that which takes place along its fellow-threads, 
that differing nervous impulses travel along different nerve-fibres, and that 
nervous and psychical events are the outcome of the clashing of nervous 
impulses as they sweep along the closely-woven web of living threads of 
which the brain is made. We have learnt by experiment and by observa- 
tion that the pattern of the web determines the play of the impulses, and 
we can already explain many of the obscure problems not only of nervous 
disease, but of nervous life, by an analysis which is a tracking out the 
devious and linked paths of nervous threads. The very beginning of this 
analysis was unknown in 1799. Men knew that nerves were the agents of 
feeling and of the movements of muscles ; they had learnt much about what 
this part or that part of the brain could do ; but they did not know that 
