12 CIRCUMSTANCES MODIFYING THE ACTION OF DRUGS 



sired. The medicinal solution should be free from solid particles and 

 microorganisms. If the solution is not clean, or is irritating, abscess may 

 occur. The syringe and needle must also be absolutely clean. Solutions 

 made by dropping tablets in pure drinking water will rarely cause 

 abscess, and the syringe may be made aseptic by filling it with alcohol 

 (70 per cent.) and wiping the needle with the same, previous to their 

 employment. Solutions may be preserved for hypodermatic use with 

 boric acid (1 per cent.), but soluble tablets are more convenient. 



In practising this method the hair should be removed from the seat 

 of injection — preferably the thin skin underlaid by connective tissue 

 behind the elbow or on the abdomen — and the part washed with water 

 followed by alcohol; then a loose fold of skin is picked up and held 

 firmly_ between the thumb and forefinger of the left hand, while the 

 needle is thrust under the skin, but not into a vein. The syringe is 

 slowly emptied and the needle withdrawn, keeping slight pressure over 

 the point of inj ection with the thumb for a few seconds. The use 6i irri- 

 tating drugs- — permissible in emergencies — as ether and ammonia, is less 

 apt to be followed by abscess if injected deeply into the muscular sub- 

 stance, and absorption is more rapid and painless, than when given 

 subcutaneously. 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 drams for horses, although large amount?' 

 of salt solution may be injected into the subcutaneous tissue or muscles 

 (hypodermoclysis) with great benefit in hemorrhage, etc. (See p. 519.) 



The minimum doses of drugs should be employed by the subcuta- 

 neous method. 



The indications for subcutaneous injection are: 



(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, anesthesia, 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 strychnine in roaring and other local paralyses; atropine in local 

 muscular spasms; veratrine in muscular rheumatism; intraneural injec- 

 tions of alcohol for neuralgia. 



4. Intratracheal injection is a strictly veterinary procedure. The 

 skin is incised aseptically with a sharp scalpel midway in the neck, and 

 a stout needle (attached to a syringe) is thrust between the rings into 

 the trachea. Larger quantities [H., §i-ii (30-60 mils)] and more irritat- 

 ing drugs are given in this way than by the subcutaneous method, and ab- 

 sorption is about as rapid; the dose is the same. There is undoubtedly 



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