OF THE CENTRAL MOTOR INNERVATION OF THE LARYNX. 
193 
bulb were placed 1 mm. apart. The stimulus was kept applied to the cortex for 
different periods of time according to varying cii'cumstances. Thus if a very minimal 
stimulus was being employed it was necessary, in order to judge of its effect upon the 
cortex, to prolong the excitation during several respiratory movements of the vocal 
cords, i.e., from 5 to 10 seconds. If, however, the stimulus was markedly adequate 
so that an unmistakeable effect w^as produced immediately and ceased directly the 
stimulation was discontinued, then the application of the electrodes was only main¬ 
tained for from 1 to 2 seconds, so as not to exhaust the cortex. 
2. Operative techniciue .—The first point to be considered of course is the anses- 
thesia, the importance of which has been already alluded to, and is considered in 
further detail on p. 195. We may say at once that we have almost invariably used 
ether, in a few cases also in part chloroform ; but inasmuch as the latter did not show 
any specific effect, differing much from that of ether, it is sufficient only to allude to it 
here as it may chance to be mentioned hereafter. The narcotisation was always con¬ 
ducted in the following manner :—The ether was first given by inhalation, and then 
complete unconsciousness having been produced tracheotomy was next performed and 
the anaesthetlsation continued through a funnel and short* piece of rubber tubing, 
the funnel resting on cotton wool wet with ether and covered with a cloth. This 
method had the advantage that as it was usually found far more convenient to inspect 
the larynx from below all trouble connected with the inhalation of the narcotic was 
avoided, and as the trachea was always completely divided it was readily moved 
aside without twisting the larynx to eltlier side, and consequently an uninterrupted 
view obtained. Furthermore, if too much anaesthetic was given by mistake, it was 
easy to restore the animal by inflation. 
The tracheotomy having been done, as large a cannula as possible was inserted and 
fitted as above stated. 
The animal was secured in a prone position and the operation proceeded with to 
expose the central parts of the brain. These may be referred to as cortex, corona 
radiata, internal capsule, and bulb. The second and the third of course consist only 
of fibres, whereas in the first and last case additional complications arise and extra 
precautions have to be taken owing to their being central apparatuses. 
Cortex ,—The anterior third of the skull, including the roof of the orbit, was then 
removed by first making a trephine opening and subsequently removing the bone piece¬ 
meal with fine bone forceps. All bleeding from the bone, which was always free, was 
immediately checked by wax. In this way the whole of the anterior extremity of the 
hemisphere, including the orbital surface, was completely exposed, i.e., as far as the 
margin of the olfactory tract. For the better exposure of the same the tissues filling 
the orbit were drawn forward, the ocular contents having previously been removed 
from the eyeball through an incision in the sclerotic.f By means of constant irrigation 
* Purposely short to allow of proper change of the respiratory gases in ventilation of the lungs. 
t Or the eyeball removed (Hitzig). 
MDCCCXC.—n. 2 c 
