8 CIECUMSTANCES MODIFYING THE ACTION OF DRUGS 



but not into a vein. The syringe is slowly emptied and 

 the needle withdrawn, keeping slight pressure over the 

 point of injection with the thumb for a few seconds. The 

 use of irritating drugs— permissible in emergencies — as 

 fluid extract of ergot, tincture of digitalis, ether and 

 ammorfia, is less apt to be followed by abscess if injected 

 deeply into the muscular substance, but this method causes 

 more pain than ordinary injections. To avoid getting air 

 in the veins, all the air is removed from the syringe before 

 using, by holding it, needle upwards, and pushing in the 

 plunger till a few drops of the solution are forced out of the 

 needle. The danger of introducing air into the blood stream 

 is greatly exaggerated, however, as the writer has proved by 

 forcing vast quantities of air into the jugular vein of a horse 

 without producing any untoward symptoms. The proper 

 quantity of a solution for subcutaneous use is 5-30 minims 

 for dogs ; 1-2 drachms for horses, although large amounts 

 of salt solution may be injected into the subcutaneous tissue 

 or muscles (hypodermoclysis) with great benefit in haemor- 

 rhage, etc. See p. 735.) 



The minimum doses of drugs should be employed by 

 the subcutaneous method. 



INDICATIONS FOR SUBCUTANEOUS INJECTION. 



(a) To secure a rapid action, as in relieving intense pain or motor 

 excitement ; and to support a failing heart, respiration and vascular 

 tone in severe operations, anaesthesia, or other poisoning. 



(b) When administration of drugs by the mouth is inadvisable or 

 impossible, as in unconsciousness, dysphagia, convulsions or vomiting. 



(c) When a local as well as general action is beneficial, e.g., the 

 use of strychnin in roaring and other local paralyses ; atropin in local 

 muscular spasms ; veratrin in muscular rheumatism. 



4. Intratracheal injection is a strictly veterinary pro- 

 cedure. The skin is incised aseptically with a sharp scalpel 

 midway in the neck, and a stout needle (attached to a syringe) 

 is thrust bjtween the rings into the trachea. Larger quan- 

 tities [H. ( 5 i.-ii.) (30.-60.)] and more irritating drugs are 

 given in this way than by the subcutaneous method, and 

 absorption is about as rapid ; the dose is the same. There 



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