THE CENTRAL NERVOUS SYSTEM 389 



Many skin areas are supplied by fibres from at 

 least two sensory roots. The fields of distribution 

 overlap. 



MUSCULAR TONUS 



Brondgeest'a Experiment. Fasten a lightly 

 etherized frog back uppermost on the frog-board. 



In a line between the ilium and the coccyx 

 open the pelvic cavity by cautiously dividing the 

 skin, fascia, and muscle. Divide the sciatic nerve 

 roots on the operated side. Pass a hook or thread 

 through the jaw and hang the frog up. 



Observe that the limb the nerves of which 

 have been cut is relaxed, so that the toes hang 

 lower than those of the limb which still retains 

 its connection with the central nervous system. 



APPARATUS 



Normal saline. Bowl. Towel. Pipette. Stand. 

 Muscle clamp Bent hook. Inductorium. Dry cell. 

 Electrodes. Large brass electrodes. Cotton. Key. 

 Frog-board. Fine copper wire. One-half per cent solu- 

 tion of strychnine sulphate. Glass jar with ether and 

 sponge. Balancing board. Strong acetic acid. Filtei 

 paper. Evaporating basin. Wire gauze. Bunsen burner. 

 Thermometer. Dilute sulphuric acid (0.2 per cent). 

 Beaker Kymograph. Electro-magnetic signal. Tuning 

 fork. Pole-changer. Vertebral saw. 



