214 DIGESTION. [CHAP, xxiv 



occurrence of vomiting when the abdominal muscles and diaphragm 

 have been paralysed, or its occurrence when an inert bag, as a 

 pig's bladder has been substituted for the stomach, the external 

 muscles being intact (as in Majendie's noted but most cruel expe- 

 riment), lead to no conclusion, for, in the one case the violence 

 done so impairs the conditions necessary for the act (both nervous 

 and muscular) that it cannot be expected to take place ; and in the 

 other, the substitution of the inert bag, and the section of the 

 oesophagus, are favourable to the escape of fluids from the former 

 and through the latter, under the slightest pressure. 



The nervous changes which take place in the act of vomiting are 

 of the most interesting kind. It must be borne in mind that this 

 act may take place 1st. from the introduction of certain sub- 

 stances into the stomach, some of which, as bile, mustard, common 

 salt, not becoming absorbed, must act simply by the impression 

 they make on the mucous membrane; 2. by the introduction of 

 emetics, as tartar emetic, into the blood, or by the presence of 

 certain morbid poisons in that fluid ; 3. by mental emotion, as 

 that excited by the sight of a disgusting object; 4. by irritation 

 at the base of the brain. Vomiting may be caused, therefore, 

 either by the direct application of a stimulus to the gastric surface, 

 or by the disturbance of some part of the brain through the pre- 

 sence of particular substances in the blood, that is, by causes 

 operating from periphery to centre, or by causes acting directly 

 on the centre itself. Either the disturbing cause, as tartar emetic 

 in the blood, affects the medulla oblongata, in which are implanted 

 the vagi nerves ; or some of the fibres of these nerves propagate 

 to the centre the effects of the peripheral irritation of the gastric 

 mucous membrane. When the medulla oblongata is thrown into 

 excitement by any of the causes abovementioned, certain motor 

 nerves implanted in it are stimulated to action, and the abdominal 

 muscles, the diaphragm, and the muscles of the larynx as well as 

 the muscular fibres of the stomach and oesophagus, are thrown 

 into that combined action which is essential to the production of 

 active vomiting. 



When vomiting is the result of a peripheral stimulation, it 

 affords a remarkable example of a reflex or physical nervous action 

 of the most complex kind, in which; from the excitation of a few 

 sentient nerves, the nervous force is made to radiate upon several 



protruded. For half an hour it was seen repeatedly and forcibly contracting 

 itself, till by its own efforts it expelled all its contents except the gases. 

 See Paget's Report for 1845. 



