1883.] On the Motor Roots of the Brachial Plexus, fyc. 231 



experimented on four monkeys. The animals were thoroughly 

 narcotised with chloroform, and kept so during the whole course of 

 the experiments. The posterior roots of the nerves under investiga- 

 tion were cut, and the anterior stimulated within the vertebral canal, 

 with a weak induced current from the secondary coil (distant 20 — 15 

 centims.) of a Du Bois Reymond's magneto- electromotor and one 

 Daniell. As in former experiments, a large flat electrode was placed 

 on the sacrum as a neutral poiat, the exciting electrode being a 

 hooked needle, by means of which the roots could be easily insulated 

 and separately stimulated. 



In the first experiment I failed to obtain dilatation of the pupil 

 from stimulation of the spinal roots from the second dorsal up to the 

 fourth cervical, though the functional activity of the roots was 

 indicated by movements of the limb. In the second I exposed the 

 dorsal roots from the eighth up to the third inclusive. Though 

 different strengths of current were tried no change in the pupil 

 occurred, unless when the current was so strong as to cause diffuse 

 stimulation. In such case both pupils would occasionally become 

 dilated, as under sensory stimulation in general. The functional 

 activity of the roots under investigation was shown by contraction of 

 the thoracic muscles on the side of stimulation. 



In the third experiment, however, results were obtained of such 

 definiteness and uniformity, as to indicate almost without further 

 confirmation the origin of the dilator nerve of the iris. 



In this experiment the spinal nerves were exposed from the sixth 

 cervical to the eighth dorsal inclusive. The posterior roots were cut 

 on the left side, and the anterior roots stimulated, while the eyes were 

 carefully observed by two assistants — my pupils, Mr. Norvill and 

 Mr. East. Dilatation of the left pupil occurred almost invariably , on 

 stimulation of the second dorsal root, whereas no change whatever 

 could be perceived on stimulation of any of the other exposed roots. 

 This was verified over and over again, and the several roots repeatedly 

 compared with each other. 'The distance of the secondary coil in this 

 experiment ranged from 20 — 18 centims. 



Stronger currents not carefully insulated caused dilatation of both 

 pupils wherever the stimulation was applied, an expression only of 

 general sensory stimulation. 



After death a careful dissection was made for me by Mr. Brooks, 

 and the effective root, which was marked, proved to be the second 

 dorsal. An examination with a lens showed that the fibres of the 

 posterior root of this nerve had been completely severed. 



The results of the third experiment were entirely confirmed by the 

 fourth, which was carried out alike in every detail. 



In this I exposed the spinal nerves from the seventh cervical to the 

 fourth dorsal, and cut the posterior roots on the left side. 



