493 HANDBOOK OF PHYSIOLOGY. 



(3.) The Accelerator centre for the heart. A centre from which arise 

 the accelerator fibres of the heart, probably exists in the medulla. It is 

 automatic but not tonic in action. 



(4.) The Vaso-motor centre, which controls the unstriped muscle of 

 the arteries, is also situated in the medulla. Like the respiratory centre, 

 it is bilateral. 



As has already been pointed out, this centre may be directly or re- 

 flexly stimulated, as well as by impressions conveyed downwards from 

 the cerebrum to the medulla. The condition of the blood circulating ID 

 it is the direct stimulus. Its influence is no doubt a tonic or else a 

 rhythmic one. It is also supposed that there is in the medulla a special 

 vaso-dilator centre, not acting tonically, stimulation of which produces 

 vascular dilatation. The diabetic centre is probably a part of the vaso- 

 motor centre, at any rate stimulation of it causes dilatation of the vessels 

 of the liver. 



(5.) A chief centre for the secretion of Siveat exists in the medulla. 

 It controls the subsidiary spinal sweat centres. It is double, and the two 

 sides may be excited unequally so as to produce unilateral sweating. It 

 is probably automatic and reflex. 



(6.) A Spasm centre is said to be present in the medulla, on the 

 stimulation of which, as by suddenly produced excessive venosity of 

 the blood, general spasms of the muscles of the body are produced. 



(c.) Control centres. These are centres whose influence maybe 

 directed to controlling the action of the subsidiary centres. They are 



(1.) The Respiratory centre, which probably controls the action of 

 other subordinate centres in the spinal cord. ' 



(2.) The Cardio-Inhibitory, which acts upon a local ganglionic 

 mechanism in the heart. 



(3.) The Accelerator centre, if it exists, probably acts through a local 

 mechanism in the heart. 



(4.) The Vaso-motor centre controls spinal as well as local tonic 

 centres. 



(5.) The medullary Sweat centre controls spinal sweat centres. 



(d.) Tonic centres. Of the centres whose action is tonic or con- 

 tinuous up to a certain degree, may be cited the vaso-motor and the 

 cardio-inhibitory. 



It should not be forgotten that in the medulla are the centres for the 

 special senses, Hearing and Taste, and that other special centres are 

 supposed to be localized there, of which may be mentioned one, the 

 hypothetical Inhibitory heat centre, which controls the production of 

 heat by the* tissues, independently of the vaso-motor centre. 



Though respiration and life continue while the medulla oblongata is 

 perfect and in connection with the respiratory nerves, yet, when all the 

 brain above it is removed, there is no more appearance of sensation, or 



