;68 A MANUAL OF PHYSIOLOGY 



end, and reflex movements will occur. Stimulate the peripheral end : 

 no effect is produced. Now cut away the exposed posterior roots 

 and isolate and ligature two of the anterior roots, which are smaller 

 than the posterior. Stimulate the central end of one : there is no 

 effect. Stimulation of the peripheral end of the other causes con- 

 tractions of the corresponding muscles. 



2. Reflex Action : Inhibition of the Reflexes. Pith a frog (brain 

 only). Pass a hook through the jaws. Holding the frog by the hook, 

 dip one leg into a dilute solution of sulphuric acid ('2 to -5 per cent.), 

 and note with the stop-watch the interval which elapses before the 

 frog draws up its leg (Tiirck's method of determining the reflex time). 

 Wash the acid off with water. Now touch the skin of one thigh with 

 blotting-paper soaked in strong acetic acid. The leg is drawn up, 

 .and the foot moved as if to get rid of the irritant. If the leg is held, 

 the other is brought into action. Immerse the frog in water to wash 

 away the acid. Again dip one leg into the dilute sulphuric acid, and 

 estimate the reflex time. Then apply a crystal of common salt to 

 the upper part of the spinal cord. If the opening made for pithing 

 the frog is not large enough to enable the cord to be clearly seen, 

 enlarge it. Again dip the leg in the dilute acid. It will either not be 

 drawn up at all, or the interval will be distinctly longer than before. 



3. Action of Strychnia. Pith a frog (brain only). Inject into 

 one of the lymph sacs three or four drops of a o'i per cent, solution 

 of strychnia. In a few minutes general spasms come on, which have 

 intermissions, but are excited by the slightest stimulus. The extensor 

 muscles of the trunk and limbs overcome the flexors. Destroy the 

 spinal cord ; the spasms at once cease, and cannot again be excited. 



4. Excision of Cerebral Hemispheres in the Frog (Fig. 273). 

 Anaesthetize a frog lightly by putting it under a bell-jar or tumbler with 

 a small piece of cotton-wool soaked in ether. Then, holding it in a 

 cloth, make an incision through the skin overthe skull in the mesial line. 

 With scissors open the cranium about the position of a line drawn at 

 a tangent to the posterior borders of the two tympanic membranes. 

 Remove the roof of the skull in front of this line with forceps, scoop 

 out the cerebral hemispheres, and sew up the wound. As soon as 

 the animal has recovered from the ether, the phenomena described 

 at p. 739 should be verified. The frog will still swim when thrown into 

 water, will refuse to lie on its back, and will not fall if the board on 

 which it lies be gradually slanted. Let the frog live for a day, keeping 

 it in a moist atmosphere ; then expose the br'am again, determine the 

 reflex time by Tiirck's method; apply a crystal of common salt to 

 the optic lobes, and repeat the observation. The reflex movements 

 will be completely inhibited or delayed. Remove the salt, wash with 

 normal saline, excise the optic lobes, and see whether the frog will 

 now swim. 



5. Excision of the Cerebral Hemispheres in a Pigeon. Feed a 

 pigeon for two or three days on dry food, etherize it by holding a 

 piece of cotton-wool sprinkled with ether over its beak, or inject into 

 the rectum \ gramme chloral hydrate. The pigeon being wrapped 

 up in a cloth, and the head held steady by an assistant, the feathers 



