694 PHYSIOLOGY. 



irritation with electricity to the substance of the pons causes general 

 epileptiform movements in the animal. Nothnagel, by irritating with 

 the needle, has defined the limits of the spasmodic territory, or region 

 of cramps. This convulsive center is irritated by excess of C0 2 in 

 the blood, or else by absence of the proper proportion of oxygen. Oil 

 of absinthe is capable of irritating this center. 



Cerebral Peduncles. The cerebral peduncles contain all of the 

 fibers of sensation and motion in the body and direct them (except 

 a few) toward the large ganglia at the base of the brain. Stimulation 

 of a peduncle produces pain and contractions in the opposite half of 

 the body; section or deep lesion from disease produces paralysis and 

 anaesthesia in the opposite half of the body. 



The cerebral peduncles, therefore, carry: (1) the voluntary exci- 

 tations to the nerves of motion and so to the muscles; and (2) the 

 sensitive impressions made upon the peripheral extremities of the 

 centripetal nerves up to the brain. 



I have found in the cat that mechanical irritation of the locus 

 niger will cause the bladder to contract, indicating a high detrusor 

 center. Mechanical irritation of any part of the brain in front of this 

 point has no effect on the bladder. 



In the greater number of unilateral lesions of the cerebral pe- 

 duncle the so-called movement in a circle is observed. That is, the 

 animal walks or flies, but always follows the curve of circumference. 

 This is usually to the side opposite the lesion. 



Corpora Quadrigemina. In man atrophy of the opposite anterior 

 quadrigeminal body follows removal of an eye. The anterior quad- 

 rigemina are also centers for the reflex movements of the iris. As the 

 student already knows, the pupil contracts in the presence of strong 

 light, but enlarges in a faint light or darkness. If the anterior quad- 

 rigeminal bodies be destroyed, the pupil remains immovable and 

 dilated even in the presence of a strong light. 



Besides these functions for the eye, the quadrigeminal bodies are 

 believed to serve other reflex -actions. The posterior quadrigeminal 

 bodies are pathways of auditory fibers. They are also regarded as 

 centers of coordination of movements; their destruction is accom- 

 panied by disturbances of motility. 



Physiology of the Optic Thalami and Striated Bodies. 



The optic thalami, if deeply stimulated or injured, appear to be 

 but slightly irritable and little or not at all sensitive. The animal 

 has shocks or shrinkings, but does not cry out. A deep lesion, made 



