EMETICS: VOMITING. 415 



CHAPTER IV. 



EMETICS AND VOMITING. 



I. PHYSIOLOGICAL RELATIONS. 



VOMITING is a complex act, in which the respiratory muscles, 

 the abdominal walls, the walls of the stomach, the sphincter 

 of the cardiac orifice, and the oesophagus and pharynx par- 

 ticipate. Occasionally it is to he regarded as a strictly 

 physiological process for removing excess of food from the 

 stomach, as in the regular sickness of infants after a full meal 

 of milk. It is determined and directed hy an elaborate nervous 

 mechanism, consisting of a special centre, the vomiting centre, 

 in the medulla ; of afferent nerves from the fauces, stomach, 

 abdominal viscera, and peritoneum, the chief of which are the 

 glosso-pharyngeal, vagus, and sympathetic, and, indeed, from 

 other parts of the body the sensory nerves generally ; and of 

 efferent nerves (the vagus, phrenic, and intercostals) to the 

 muscles, cardiac orifice, and certain associated parts to be 

 presently mentioned. Vomiting may be induced by impressions 

 originating in the areae supplied by any of the afferent nerves ; 

 by stimulation of the centre by certain substances which reach 

 it through the blood ; or by the downward flow to it of certain 

 mental impressions, such as nauseous tastes, foul smells, dis- 

 gusting or terrifying sights, and depressing ideas. 



With the evacuation of the stomach there occur certain 

 associated acts which are of great importance to the thera- 

 peutist. A flow of saliva may precede vomiting, as is well 

 seen in some reflex cases. The gall bladder may be forcibly 

 emptied of bile, which regurgitates into the stomach and 

 is vomited. Expiratory movements, such as sneezing and 

 coughing, frequently occur at the beginning of sickness, in- 

 dicating the spread of the stimulant impressions to the asso- 

 ciated respiratory centre in the medulla; and it must be 

 carefully observed that an expiratory effect is also produced by 

 compression of the chest during the evacuation of the contents 

 of the stomach, as well as at the end of the act, when the air is 

 forcibly expelled through the larynx to prevent the entrance of 

 solid particles. Thus vomiting tends to empty the respiratory 

 passages, as well as the upper part of the alimentary canal. The 

 stimulant effect of emetics on the salivary flow is frequently 

 accompanied by a secretion of bronchial mucus ; and this being 

 expelled by the upward current of air, tends further to clear 

 the passages. 



