32O PRACTICAL PHYSIOLOGY. [LXVIII. 



removed to the skin on the inner side of the thigh. At once 

 the leg on that side is violently drawn up, perhaps both legs are 

 drawn up, and the foot of the leg first drawn up is swept over the 

 spot stimulated, as if to remove the piece of paper, i.e., purposive, 

 co-ordinated movements are executed. At once dip the frog in 

 water to remove the acid ; allow it to rest for some time. It is 

 much easier to obtain irradiation of the reflex movements by 

 chemical than by mechanical stimuli. 



(6.) After five minutes repeat the experiment, but hold the leg 

 to which the acid is applied. Probably the other leg will move, 

 and the opposite foot will remove the irritating acid paper. Wash 

 the frog and allow it to rest. 



(c.) Test further, by applying papers to the flank, the skin over 

 the gastrocnemius, &c., and in all cases characteristic but different 

 reflex movements will be elicited, if sufficient interval for recovery 

 (five minutes at least) be allowed between the successive experi- 

 ments. 



(d.) Destroy the spinal cord, all reflex action is abolished. The 

 nerves and muscles retain their excitability and the heart continues 

 to beat. Expose the heart : it beats. Muscle and nerve respond 

 to electrical and other stimuli. 



5. Action of Strychnine. 



(a.) Using a frog with its brain destroyed, inject with a fine glass 

 pipette or a hypodermic syringe into the dorsal lymph sac a drop 

 of dilute solution of acetate of strychnine (0.5 per cent.). 



(6.) Observe that as soon as the poison is absorbed i.e., within 

 a few minutes cutaneous stimulation of any part of the body, 

 even tapping the table, excites general violent tetanic spasms, and 

 not co-ordinated muscular responses, of the whole body. During 

 the convulsive paroxysm the limbs are extended, hard, and rigid, 

 while the trunk is similarly affected. The extensor muscles are 

 more affected than the flexors. The tetanic paroxysm passes off, 

 to be soon followed by another on the slightest stimulation. 

 The excitability has been so greatly increased that even the 

 slightest stimulus applied to the skin discharges a reflex spasm, 

 i.e., provokes muscular responses which are maximal, so that a 

 minimal stimulus produces a maximal response. 



(c.) Destroy the spinal cord with a seeker or long pin. At 

 once the spasms cease. Strychnia, therefore, acts on the cord 

 directly, and not on the muscles and nerves. 



(d.) In another frog, divide the cord below the bulb, the brain 

 in front being destroyed, but the cord intact. Apply a crystal 

 of sulphate of strychnia to the cord. It soon causes tetanic 

 spasms, thus showing that strychnine affects the cord. 



