750 



THE CEREBRAL CORTEX. 



should be a difference in the latency periods of the two. I have 

 accordingly put this point to the test by the following method : l Two 

 pairs of fiat electrodes, carefully guarded with paraffin, are applied 

 through trephine openings, the one to the frontal area, the other either 

 to the occipital lobe or to the superior temporal gyms. The wires 

 from the electrodes (Fig. 341, FT., Occ.) pass to a switch (Sw.), by turning 



FIG. 341. Diagram of the arrangement of apparatus for determining the comparative 

 latency periods of two parts of the cerebral cortex. G, Grove battery working the 

 Ruhmkorff coil ; D, Daniell cell working the du Bois coil, D.B.\ &.(?., short circuit 

 for du Bois coil. Zf, Helmholtz key arranged so that the Ruhmkorff circuit is made 

 at the same instant that the short circuit of the du Bois coil is broken. The other 

 parts of the diagram are described in the text. 



which the areas under investigation can be alternately stimulated. The 

 lateral movement of one of the eyes is recorded by attaching it by a 

 thread (T) to an aluminium lever (L), through which sparks at the 

 rate of 250 per second can be transmitted from a Ruhmkorff coil (JR) to 

 the smoked paper on a rotating brass cylinder (Cy.). The sparks are 



FIG. 342. Curves showing the comparative periods of latency for the ocular muscles, 

 on stimulation of the frontal and occipital cortex respectively. 



only allowed to commence from the moment of stimulation, and serve 

 to mark the time as well as the curve described ; for the lever is not 

 allowed to touch the cylinder, differences in friction against the paper 

 being thus eliminated an important point when dealing with the 

 latency of- comparatively weak muscles. 



The accompanying figure (Fig. 342) shows some of the tracings thus 

 obtained from alternate stimulation of the frontal and occipital cortex ; 



1 Internal. Monthly Journ. Anat. and PhysioL , Leipzig, 1888, vol. v. p. 149. 



