412 PHYSIOLOGY CHAP. 



The activity of the bulbar centres is for the most part deter- 

 mined by peripheral excitations that reach them by afferent paths 

 (reflex centres), but it is sometimes evoked by rhythmic or tonic 

 internal central excitations (automatic centres). Their normal 

 function depends on their structure and on the normal gas 

 exchanges kept up by circulation and respiration. Asphyxia, 

 rapid anaemia, rise of blood temperature from any cause excites 

 and finally exhausts the bulbar centres. 



In discussing the visceral functions we dealt with the bulbar 

 centres by which they are controlled, that is, those which regulate 

 cardiac activity, vasomotor tone, respiratory rhythm and digestion, 

 consequently we need only now consider their more general 

 functions. 



In the bulb, and intimately connected with the respiratory 

 centre, there is a centre which, when excited, produces general 

 convulsions or spasms. It has long been known that excitation 

 of the bulb by any kind of stimulus readily induces general con- 

 vulsions. Acute asphyxia, rapid ligation of the two carotids and 

 vertebral arteries, rapid bleeding, or compression of the veins of 

 the neck so as to produce a cerebral congestion all conduce to 

 more or less general cramps or convulsions (Kussmaul and Tenner, 

 Landois, Hermann, and others) by interruption of the normal 

 exchanges. If the interruption develops slowly the animal may 

 perish from asphyxia without any previous convulsions. 



Kussmaul and Tenner believed that they had demonstrated 

 the integrity of the bulb to be an essential condition for the 

 appearance of general convulsions, because general convulsions no 

 longer set in in rabbits after separation of the bulb from the cord. 

 Destruction of the nceud vital of Flourens was sufficient to cause 

 the animal's immediate death without convulsions. If it were kept 

 alive by artificial respiration with the bellows, no abrupt suspension 

 of gas exchanges, however produced, was capable of evoking such 

 excitation of the spinal cord as to cause general convulsions. 

 Hence, they concluded, there must be a centre in the bulb whose 

 excitation is indispensable for producing spread of convulsions to 

 all the muscles. 



Freusberg (1875), however, with dogs saw that even in the 

 " spinal " animal the hind-limbs and tail were convulsed during 

 acute asphyxia, though to a less degree than when the bulb remained 

 connected with the cord. Baglioni and Carincola (1911) confirmed 

 Freusberg's observations on pigeons. They also found that these 

 symptoms of excitation did not occur if all the posterior roots had 

 previously been divided. They are not, therefore, according to 

 Baglioni, due solely to increased venosity of the blood, as 

 Freusberg surmised, but are partly due to sensory excitations 

 carried from the periphery by the posterior roots. 



Nothnagel, by direct excitation of the rabbit's bulb, endeavoured 



