518 PHYSIOLOGY CHAP. 



voice-production intact, while section behind it abolishes phonation. 

 He further observed a cataleptic condition in monkeys after section 

 in front of the mesencephalon ; reflex movements are carried out 

 with extreme slowness, and the attitudes assumed or passively 

 given are long sustained. He holds it probable that the tonic 

 spasms of epilepsy are due to excitation of the brain-stem, which 

 agrees with Ziehen's view that they are subcortical, while the 

 clonic spasms are cortical in origin. Verworn (1898) showed that 

 after decerebration it is much easier to evoke the state of forced 

 immobility known as hypnosis in the pigeon. 



Sherrington (1898) described the persistent tonic spasm that 

 occurs in certain groups of muscles, after section of the brain in 

 front of the corpora quadrigemina, as decerebrate rigidity. This 

 symptom appears in apes, dogs, cats, rabbits, and guinea-pigs. 

 The contracted groups of muscles are the retractors of the head 

 and neck, the muscles of the tail, the extensors of the elbow, knee, 

 shoulder, and ankle. The foot and hand are but little concerned, 

 the ringers and toes not at all. In kittens this spasm may last 

 four days with little interruption. When it ceases it can easily be 

 evoked again by passive movements of the corresponding joints. 

 At first the spasm assumes the form of tonus ; subsequently it 

 becomes a tremor. In narcosis it dies down, and reappears as this 

 passes off. 



The spasm depends on the integrity of the dorsal spinal roots. 

 In fact it does not appear, or only imperfectly, in the limits to 

 which the dorsal roots had been cut some days previously, and 

 it disappears if they are divided after it has set in. 



During the state of decerebrate rigidity, stimulation of various 

 points of the central nervous system or of certain peripheral 

 nerves elicits reflexes which consist in relaxation of the contracted 

 muscles and contraction of the antagonists. Prolonged stimulation 

 sometimes results in rhythmical flexion and extension of the four 

 limbs, which by their co-ordination recall the complex of move- 

 ments present in quadruped progression (Chap. VII. et. seq.~). 



After hemisection of the 'tween brain the same rigidity 

 appears, but it is far more marked on the side of the lesion 

 (Sherrington). The whole course of the effects of hemisection of 

 the mid- brain has been described by Probst (1904). 



Probst experimented on cats. After dividing the right half of 

 the mid-brain midway between anterior and posterior corpora 

 quadrigemina, he noticed the phenomena which maybe summarised 

 as follows : 



Immediately after section on the right side there is curvature 

 of the body and head to the left side, with tonic contraction of the 

 musculature of the left side of the neck. The pupils are con- 

 stricted slit-wise, and after half an hour horizontal nystagmus may 

 be seen in the left eye alone. The jaws are closed, and there is 



