internal structure of the human brain, &c. s 
The globules and elastic substance being in different pro- 
portions in different parts of the brain, have an influence upon 
the appearance put on by the coagulum, which is a source of 
deception, and makes the coagulum tear more readily in some 
directions than others, as if fibres in those directions existed, 
which is not the case. 
The parts not being of one uniform density, makes it impos- 
sible for the sharpest knife to cut evenly ; some of the globules 
must therefore be displaced, while others are not. 
When the brain is immersed in alcohol and rendered solid, 
all these deviations from the natural appearance must be 
encreased in a greater degree, since the elastic substance is 
rendered opaque by coagulation, and all appearance of glo- 
bules lost. 
To obviate these sources of error, I requested Mr. Bauer 
to examine a small portion of the human brain in a recent 
state, composed of cortical and medullary structure, which 
had been immersed in distilled water: the surface of the 
elastic substance it is true, was dissolved, but what remained 
completely preserved its transparency ; the appearance the 
surface put on when magnified twenty-five times, is seen in 
the annexed drawing, rows of globules from the circumfe- 
rence of the cortical substance are passing unbroken in straight 
lines into the substance of the medullary portion, which could 
not have been detected in any other mode of investigation. 
I shall not prosecute farther this part of my subject on the 
present occasion, but proceed to the consideration of the brain 
of fishes, (that of quadrupeds and birds being in its structure 
so similar to the human brain, as not to require any notice 
of its peculiarities to be taken ) . 
