<58o SPASM AND SWEAT CENTRE. 



In the muscles of the face, paralysed by extirpation of the facial nerve, stimula- 

 tion of the ring of Vieussens causes pseudo-motor contractions of these muscles, 

 just as stimulation of the chorda tympani causes such contractions in the paralysed 

 tongue ($.349, 4), after section of the hypoglossal nerve (Rogoivicz). 



In analysing the vascular phenomena resulting from experiments on these nerves, we must 

 W very careful to determine, whether the dilatation is the result of stimulation of the vaso- 

 dilator* or a consequence of paralysis of the vaso-constrictors. Psychical conditions act upon 

 dilator nerves the blush of shame, which is not coufined to the face, but may even 

 extend over the whole skin, is probably due to stimulation of the vaso-dilator centre. 



Influence on Temperature. The vaso-dilator nerves obviously have a considerable influence 

 ,.n the temperature of the body and on the heat of the individual parts of the body. Both 

 vascular centres must act as important regulatorv mechanisms for the radiation of heat through 

 the cutaneous vessels ( 214, II. ). Probably they are kept in activity reflexly by sensory nerves. 

 I >i.turbancesin their function may lead to an abnormal accumulation of heat, as in fever ( 220), 

 or to abnormal cooling ( 213, 7). Some observers, however, assume the existence of an in- 

 tracranial "heat-regulating centre " {Tschctschichin, Naunyn, Quincke). According to Wood, 

 separation of the medulla oblongata from the pons causes an increased radiation and a diminished 

 production of heat, due to the cutting olf of the influences from the heat-regulatiug centre ( 377). 



373. SPASM-CENTRE SWEAT-CENTRE. Spasm-Centre. In the 



medulla oblongata, just where it joins the pons, there is a centre, whose stimulation 

 causes general spasms. The centre may be excited by suddenly producing a highly 

 venous* condition of the blood ("asphyxia spasms"), in cases of drowning in 

 mammals (but not in frogs), sudden anamria of the medulla oblongata, either in 

 consequence of haemorrhage or ligature of both carotids and subclavians (Kussmaul 

 <i,cl Tenner), and lastly, by sudden venous stagnation caused by compressing the veins 

 coming from the head. In all these cases, the stimulation of the centre is due to 

 the sudden interruption of the normal exchange of the gases. When these factors act 

 quite gradually, death may take place without convulsions. Direct stimulation by 

 means of chemical substances (ammonia carbonate, potash, and soda salts, <fcc.) applied 

 to the medulla, quickly causes general convulsions (Papellier). Intense direct 

 mecliankal stimulation of the medulla, as by its sudden destruction, causes general 

 convulsions. 



Position. Xothnagel attempted by direct stimulation to map out the position of the spasm- 

 rentre in rabbits ; it extends from the area above the ala cinerea upwards to the corpora quad- 

 rigemina, It is limited externally by the locus coeruleus and the tuberculum acusticum. In 

 the frog, it lies in the lower half of the 4th ventricle (Heubel). The centre is affected in exten- 

 sive reflex spasms ($j 364, 6), e.g., in poisoning with strychnin and in hydrophobia. 



Poisons. Many inorganic and organic poisons, most cardiac poisons, nicotin, picrotoxin, 

 ammonia ( 277), and the compounds of barium cause death after producing convulsions, by 

 acting on the spasm-centre {R'obcr, Heubel, Bbhm). 



If the arteries going to the brain be ligatured so as to paralyse the medulla oblongata, then, 

 on ligaturing the abdominal aorta, spasms of the lower limbs occur, owing to the anaemic 

 .stimulation of the motor ganglia of the spinal cord (Sigm. Mayer). 



Pathological Epilepsy. Sehroeder van der Kolk found the blood-vessels of the oblongata 

 dilated and increased in cases of epilepsy. Brown -Sequard observed that injury to the central 

 or jieripheral nervous system (spinal cord, oblongata, peduncle, corpora quadrigemina, sciatic 

 nerve) of guinea-pigs produced epilepsy, and this condition even became hereditary. Stimula- 

 tion of the cheek or of the face " epileptic zone," on the same side as the injury (spinal cord), 

 caused at once an attack of epilepsy ; but when the peduncle was injured, the opposite side 

 must be stimulated. Westphal made guinea-pigs epileptic by repeated light blows on the skull, 

 ami this condition also became hereditary. In these cases, there was effusion of blood in the 

 medulla oblongata and upper part of the spinal cord ( 375 and 378, I.). Direct stimulation 

 of the cerebrum also produces epileptic convulsions. Strong electrical stimulation of the motor 

 areas of the cortex cerebri is often followed by an epileptic attack ( 375). [It is no unfrequent 

 occurrence while one is stimulating the motor areas of the cortex cerebri of a dog, to find the 

 animal exhibiting symptoms of local or general epilepsy.] 



Sweat-Centre.- -A dominating centre for the secretion of the sweat of the 

 entire surface of the body ( 289, II.) with subordinate spinal centres ( 362, 8) 

 occurs in the medulla oblongata (Adamkiewicz, Marme, Nawrocki). It is double, 



