4i 6 MATER i A MEDIC A AND THERAPEUTICS. 



Whilst the respiratory and gastric centres are thus power- 

 fully stimulated in vomiting, the cardiac and vascular centres 

 are greatly depressed, the action of the heart and the pulse 

 "being reduced in force at least, between the acts of sickness, 

 and a sense of faintness and giddiness overspreading the 

 patient from further cerebral anaemia. At the same time, the 

 motor centres in the brain, and probably in the cord, are 

 lowered, leading to prostration and inability to support the 

 weight of the body, and compelling recumbency. Lastly, the 

 centres of perspiration are stimulated, causing the profuse 

 sweating familiar in many cases of sickness. Altogether, the 

 student will appreciate how extensive is the physiological dis- 

 turbance produced by vomiting, and how great is the influence 

 which it furnishes us over several of the most important 

 functions of the body. 



II. PHARMACODYNAMICS. 



Vomiting may be excited by certain substances and measures, 

 which are called emetics. Emetics are said to be either 

 (1) direct, when they act upon the stomach itself ; or (2) indirect, 

 when they act upon the vomiting centre or some other part of 

 the nervous mechanism. Direct emetics are the larger of the 

 two classes. They include warm water, Infusion of Chamomile, 

 Salt and Water, Mustard, Carbonate of Ammonia, Sulphate of 

 Zinc, Alum, and Sulphate of Copper. They are necessarily 

 given by the mouth. Indirect emetics are a small group of drugs, 

 including only Ipecacuanha, Antimony, and Apomorphia. 

 These excite vomiting by whatever channel they may be ad- 

 mitted into the blood subcutaneously, by the mouth, or by 

 the rectum. For the same reason they produce greater 

 general depression, that is, depress the other vital centres 

 in the medulla more than moderate doses of the direct 

 emetics. Physical irritation of the fauces is a ready emetic 

 measure of the indirect class; and nauseous drugs, such as 

 castor oil and rhubarb, frequently act on the nerves of the 

 same part, but are not given with this intention. Ipecacuanha 

 and Antimony act on the stomach as well as on the centre, and 

 are really, therefore, direct and indirect emetics. 



The means at our disposal for averting or arresting vomiting 

 are as various as the parts of the extensive mechanism upon 

 which they act. They may be called anti-emetics. First of 

 these may be mentioned the measures which reduce the irri- 

 tability of the vomiting centre, such as the recumbent posture, 

 nourishing food, Amyl-Nitrite, Nitro-Glycerine, Alcohol, 

 Opium, Chloral, the Bromides, and Diluted Hydrocyanic Acid. 

 A second class, more readily available, comprise the sedatives of 



