124 DONALDSON. [Von. IX. 
generally employed; and second, in the light of these facts to 
discover, perhaps, some method which will leave the tissues 
more nearly normal than do those which are now employed. 
It is to the former object alone that we shall here attend. 
The tissue which we have chosen for the subject of experi- 
ment is that forming the central nervous system of the 
vertebrates, and the chief observations have been directed to 
the change in the weight and volume and to the variations in 
solids and fluids while undergoing the hardening process. 
The extent and importance of these changes were brought 
to our attention several years since, when the brain of Laura 
Bridgman was put into our hands for examination. 
The brain had not been weighed upon its removal from the 
body, and it was thought desirable, if possible, to determine its 
weight when fresh. 
This brain had been subjected for 45 days to Miiller’s 
fluid to which had been added } its volume of 95% alcohol, 
and then to a solution of 25% bichromate of potash for 44 days 
more, before it was tested with a view to obtaining its fresh 
weight. 
Control experiments, made upon other brains, indicated a 
very great increase in weight as the result of a treatment 
nearly similar to that to which the Bridgman brain had been 
subjected. Following this hint, a somewhat more extensive 
series of observations was undertaken to determine the condi- 
tions controlling this increase in weight, and these observations 
furnish the material for this present paper. The standpoint 
from which they have been made has been rather chemical and 
physical than histological, and we have not prepared specimens 
for the microscope from material hardened in different ways, 
because, until the number of methods of hardening shall have 
been reduced to a minimum by means of some preliminary 
work, this latter point cannot be advantageously taken up. 
History of Investigation. — The investigation was begun in 
January, 1890, at Clark University, Worcester, Mass. In con- 
nection with it, that Institution granted an appropriation for 
the study of the nervous tissues in man, and during the month 
of September, 1890, through the courtesy of Dr. Ferguson, the 
