A16 Prof. G. Retzius. Principles of the [June 15, 
grasp of natural phenomena as well as on actual experiments and dissecting 
work. 
A more thorough knowledge of the minute structure of the brain and the 
whole nervous system was essential, if the physiology of those organs was to 
advance. To that end the perfecting of the microscope was a conditio sine 
gua non. Earlier anatomists, ¢.g., Leeuwenhoek and Malpighi, had paved the 
way, lt is true, to our present results, but did not proceed far themselves. In 
accord with the last-named great Italian scientist (Malpighi), Emanuel 
Swedenborg, though, put forward a remarkable theory regarding the 
composition of the cerebral cortex, which he—in opposition to so many 
anatomists of that day—definitely declared to be the seat of the psychical 
phenomena. 
Not until during the last century was it possible to get nearer the solution 
of this the most difficult problem of histology. It had by degrees been 
discovered that the nerve-tissues consist of nerve-cells in several different 
forms, and of nerve-fibres with and without myelin sheaths. It was also 
found out that the nerve-fibres are processes of the nerve-cells. The attempt 
was made to devise methods for tracing the nerve-fibres in their several 
courses, partly by hardening and staining them, partly by effecting their 
degeneration along certain paths, partly by studying the gradual development 
of their myelin sheaths in the embryo. By means of such researches 
scientists, before the close of the seventies, had arrived at the point of being 
able to establish theories concerning the minute construction of the nervous 
system in general. But, alas! how hypothetical, how uncertain these theories 
for the greater part were! I have still a clear remembrance of the hesitation 
and reluctance which I felt year after year, from 1877 onwards, in lecturing, 
as professor of histology, about this subject to my classes of students. I did 
not myself believe in a good deal of what I was constrained to teach them 
in accordance with the then accepted doctrines of science concerning the 
structure of the central nervous system. As a result of*the investigations 
which I conducted in conjunction with Axel Key in the years 1869 to 1876, 
into the lymphatic spaces, and the structure of the brain, and the rest of the 
nervous system, I had arrived at the conviction that the abstract theories 
then held by men of science as to the construction of that system must be 
incorrect and were inconclusive. 
It was at this period the Italian scientist Camillo Golgi made his invention 
for staining chrome-hardened nerve tissue with silver solution, by which the 
nerve-cells were selectively dyed brown. At first his communication, which 
was published in some smaller Italian journals with a very limited circulation 
in other countries, attracted very little notice, but on the appearance in 1885 
