428 
DR. A. WALLER ON THE ALTERATION OF THE 
means, aided also by the mylohyoid muscle, which is left unaffected for the same 
reason, the inner half of the tong-ue still enjoys contractile powers. 
Respii'ation is hurried and laboured, and death is the invariable result of division 
of these nerves, whether made at the spine or at the throat. In summer, the animals 
died at the end of two or three days. 
Division of a single hypoglossal only causes paralysis of the corresponding half of 
the tongue, complete when the section is near the spine, and imperfect when at the 
throat. The animals generally survive after the section of one nerve. 
The peripheric extremities of the hypoglossal nerves are most easily found at the 
inferior surface of the tongue. By removing a minute fragment at this region, we 
can observe, without any further preparation, ramifications of nerves, which are gra- 
dually reduced to a network of single tubules on the surface, among the capillary 
network. At the same time, among the muscular fibres are other ramifications, either 
crossing them in a transverse direction or running parallel. Like the former, they are 
reduced to single fibres, running in all directions without forming any free ends. It 
is at the under surface that the alterations of the hypoglossal must be studied. 
During the four first days, after section of the hypoglossal nerve, no change is ob- 
served in its structure. On the fifth day the tubes appear more varicose than usual, 
and the medulla more irregular. About the tenth day the medulla forms disorganized, 
fusiform masses at intervals, and where the white substance of Schwann cannot be 
detected. These alterations, which are most evident in the single tubules, may be 
found also in the branches. After twelve or fifteen days many of the single tubules 
have ceased to be visible, their granular medulla having been removed by absorption. 
The branches contain masses of amorphous medulla. 
We are naturally led to inquire, whether extraneous circumstances have any in- 
fluence over the removal of the tissue. We find that in the summer-time, when the 
renewal of the tissues must be considerably more active, in consequence of the in- 
creased respiration and activity of the animals experimented upon, that the altera- 
tion is more rapid than in winter, when they are in a state of torpor and hybernation. 
At present we have restricted our observations to the alterations which take place 
in the ramifications originating from two trunks, but we cannot suppose that this is 
a local phenomenon, and that other nerves do not participate in similar alterations, 
and that the brain itself, composed in great part of tubular fibres, must be excluded. 
Experiments on other nerves already enable me to affirm that such is not the case, 
and that they are to be found on other nerves, such as the sciatic, &c., and, moreover, 
that they are as extensive as the nervous system itself. It is impossible not to anti- 
cipate important results from the application of this inquiry to the different nerves of 
the animal system. But it is particularly with reference to nervous diseases that it 
will be most desirable to extend these researches. If one conviction impresses itself 
more firmly on the mind than another, it is that what we term functional diseases of 
