646 



A MANUAL OF PHYSIOLOGY 



other with the right arm or the region of the right scapula. The two 

 feet are the most unfavourable combination. 



Central Nervous System. It was discovered by du Bois-Reymond 

 fchat the spinal cord, like a nerve, shows a current of rest between 

 longitudinal surface and cross-section, and that a current of action is 

 caused by excitation. Setschenow stated that when the medulla 

 oblongata of the frog was connected with a galvanometer, spontaneous 

 variations occurred which he supposed due to periodic functional 

 changes in its grey matter. Gotch and Horsley have made elaborate 

 experiments on the spinal cord of cats and monkeys. Leading off 

 from an isolated portion of the dorsal cord to the capillary electro- 

 meter, and stimulating the motor part of 

 the cortex cerebri, they obtained a per- 

 sistent negative variation followed by a 

 series of intermittent variations. This 

 agrees remarkably with the muscular con- 

 tractions in an epileptiform convulsion 

 started by a similar excitation of the 

 cortex, which consist of a tonic spasm 

 followed by clonic (interrupted) contrac- 

 tions. 



By means of the galvanometer the 

 same observers have made investigations 

 on the paths by which impulses set up at 

 different points travel along the cord. To 

 these we shall have to refer again (p. 702). 

 Electromotive changes are said to occur 

 FIG. 214. CONSTRUCTED U1 t h e cerebral cortex, when various 

 ^oTTu/r* ^nsory "<*ves are stimulated -for ex- 

 AND LINT). ample, when the retina is excited by light. 



, But only a few experiments have hitherto 



The curves are constructed , J/L/-I -ri j -I-M i_i\ 



from the photographic records been made (by Caton, Beck, and Fleischl), 

 shown in Fig. 213. These and and it is not certain that the observed 

 ex^ t e h ssion oV Se P a h c S tuaf changes diff erences f potential have their seat in 

 of P po S tentia during "he cardiac the grey matter. They may be due merely 

 cycle. Time is laid off along t o the excitation of the white fibres. 

 foradOT^^ Glandular Currents. These have been 



same space being allotted to ten studied with any care only in the sub- 

 milKvofts {*;*., ij ff volt) as to one maxillary gland and in the skin, although 



the liver, kidney, spleen, and other organs, 



also show currents when injured. In the sub-maxillary gland the 

 hilus is positive to any point on the external surface of the gland ; a 

 current passes from hilus to surface through the galvanometer, and 

 from surface to hilus through the gland (Fig. 215). When the chorda 

 tympani is stimulated with rapidly-succeeding shocks of moderate 

 strength, there is a positive variation ; i.e., the surface becomes still 

 more negative to the hilus. This variation can be abolished by a 

 small dose of atropia, and then stimulation causes a slight negative 

 variation. A further dose of atropia abolishes this, too. With slowly- 

 interrupted shocks (not more than five per second) a large negative 



