202 PHYSIOLOGY CHAP. 



(anaesthesia of the vagi in the neck, anaesthesia of the glosso- 

 pharyngeal, anaesthesia of the pharyngo-oesophageal region) is 

 capable by itself of inhibiting evacuation of the stomach, even 

 when emetics with a central action (apomorphine) are administered. 

 This fact can be explained on the assumption that emetics with a 

 central action raise the excitability of the centre, on which the 

 normal stimuli reaching it by sensory paths can induce vomiting. 

 After complete anaesthesia of these sensory paths the hyper- 

 excitability of the centre produced by the emetic is not of itself 

 sufficient to determine vomiting. 



The action of emetics of the second category (copper sulphate, 

 tartar emetic) is transmitted solely by the vagi, hence the 

 possibility of vomiting ceases when they are divided. In some 

 cases vomiting ceases in dogs after destruction of the corpora 

 quadrigemina and the corpora striata. According to certain 

 observations incidentally made by ourselves when studying the 

 cerebellum, partial destruction of the posterior corpora quadri- 

 gemina gives rise in dogs, for 4-5 days in succession, to repeated 

 vomiting, which then ceases entirely with the disappearance of 

 the excitatory phenomena. It is clear that the emetic action of 

 these substances is mainly due to reflexes by the afferent paths, 

 whatever the situation of the part on which they act. Vomiting, 

 in fact, follows not merely when the emetic is introduced into the 

 stomach, but also when it is injected into a loop of the intestine, 

 which explains the vomiting that accompanies certain intestinal 

 diseases. 



It is still doubtful whether, in order to explain the specific 

 behaviour of the nerve centres in vomiting, we should assume the 

 existence of an isolated centre for vomiting, or a specific association 

 and co-ordination of the separate motor and inhibitory centres for 

 the different parts of the stomach as pointed out by Openchowski, 

 as well as active intervention of the bulbar respiratory centres. 

 Tumas (1887) assumed a unitary centre for vomiting, situated 

 bilaterally in the depth of the medulla oblongata near the calamus 

 scriptorius. He saw in effect that in dogs destruction of the 

 median line of this region made vomiting impossible. Openchowski, 

 on the contrary, doubted the existence of a special centre of 

 vomiting, and thought it probable that Tumas' results depend on 

 the interruption of the nerve paths which descend from the 

 corpora quadrigemina to the bulb, and thence to the anterior 

 columns of the spinal cord. 



He showed by many observations made in collaboration with 

 Hlasko, that apomorphine-vomiting is inhibited after destruction 

 of the posterior corpora quadrigemina, while that from copper 

 sulphate is violently excited. This fact shows that there must be 

 two distinct central nuclei that act as centres for vomiting. He 

 further saw that vomiting ceases immediately after the section of 



