442 Prof. G. Retzius. Principles of the [June 15, 
structure and composition of the central nervous system, there remains, 
nevertheless, an almost infinite amount to be done in this domain. Almost 
every year that passes witnesses the rise of new opinions and the dis- 
covery of new and unsuspected details of structure. For instance, who 
would have been able to foretell some years ago that in the spinal ganglions, 
which to all appearance are so comparatively simple in their structure, such 
complicated ramifications and connections would be found to exist in the 
ganglion as those which have recently been made manifest by Cajal and by 
Dogiel? There still remain without any doubt innumerable discoveries for 
coming generations in all those domains. 
The limited time for this lecture does not permit me to enter any further 
upon these fields. 
When it is remembered, however, what difficulties present themselves to 
the investigator, it is surely a matter for astonishment that our knowledge 
has been advanced in so splendid a way during the recent decades, more 
especially in the last two. This fact warrants us in cherishing the confident 
hope, that by means of sedulously pursued, thoroughgoing labour on the 
part of scientists in all civilised countries, the secrets of the nervous system 
may be brought nearer to light. Still we must not imagine that the truths 
which we believe to be established are absolutely and unalterably certain. 
In science, the famous words of Duclaux, the French scientist, will always 
remain true: 
“Ta science s’'avance parce quelle n’est sir de rien.” 
These words have a wide and profound significance. New methods, new 
researches, often teach us to see things in a new and to some extent different 
light, and may even disclose errors in results which have been long accepted 
and approved. | 
I am not myself willing to go so far as Carl Ludwig, the renowned German 
physiologist, when he said: “Die Methode ist Alles,” though I admit that 
there is a good deal of truth in his words. New and good methods carry our 
knowledge forward, but moreover the investigator requires that perseverance, 
that devotion and that critical acumen in observation, which, provided he is 
not a prey to preconceived ideas, make it possible for him to distinguish 
between appearances and reality. Hypotheses may be excellent as lodestars 
though they may on occasion lead one astray. Theories can only hold their 
ground and lay claim to consideration as long as they agree with the facts 
which have been brought to light and constitute a comprehensive summary of 
their results; if that is no longer the case they must inevitably fall and yield 
place to others, in the light of the criticism brought to bear upon them and 
in obedience to the new observations which science has made. 
