OcTOBER 6, 1899.] 
lay hold of the influences which fashion the 
garment of life. Whether the problems of 
life are looked upon from the one point of 
view or the other, we to-day, not biologists 
only, but all of us, have gained a knowl- 
edge hidden even from the philosophers a 
hundred years ago. 
Of the problems presented by the living 
body viewed as a machine, some may be 
spoken of as mechanical, others as physical, 
and yet others as chemical, while some are, 
apparently at least, none of these. In the 
seventeenth century William Harvey, lay- 
ing 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 ‘ fermenta- 
tion’ 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 
organisms. He made use of the words ‘ vital 
force’ or ‘ vital principle’ not as an occa- 
sional, 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 an- 
other ; if we use it now when we are dealing 
with the chemical and physical events of 
life, we use it with reluctance, as a deus ex 
SCIENCE. 
471 
machina to be appealed to only when every- 
thing else has failed. 
Some of the problems—and those, per- 
haps, the chief problems—of the living body 
have to be solved neither by physical nor 
chemical methods, but by methods of their 
own. Suchare 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, and es- 
pecially in the brain, which issue as feeling, 
thought and the 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-fiber differs from that which takes 
place along its fellow-threads, that differ- 
ing nervous impulses travel along different 
nervous-fibers, and that nervous and psy- 
chical events are the outcome of the clash- 
ing 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 al- 
ready explain many of the obscure prob- 
lems 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 feel- 
ing and of the movements of muscles ; they 
had learnt much about what this part or 
or that part of the brain could do ; but they 
did not know that one nerve-fiber dif- 
fered from another in the very essence of 
its work. It was just about the end of the 
past century, or the beginning of the pres- 
