HYPODERMIC AND INTRATRACHEAL INJECTIONS. 



75 



The double-acting syringe is employed in a similar way. One 

 nozzle is connected by a rubber tube with the needle inserted in 

 the vein, the other by a similar tube with the vessel containing the 

 injection fluid. After injecting the contents of the syringe into the 

 vein the two-way tap is turned and the barrel of the syringe again 

 filled by drawing back the piston. By returning the tap to its 

 original position and once more pressing down 

 the piston a second quantity is injected ; the 

 process can be repeated as often as desired. 



One of the drawbacks of intravenous in- 

 jection is the tendency to thrombosis of the 

 vein in consequence of injury to the tunica 

 intima by the needle. This danger, however, as 

 well as that of the entrance of air, can be 

 avoided by skilful manipulation. By proper 

 care in choosing the drug and carrying out the 

 above manipulation bad results are avoided. 



(b) In subcutaneous or hypodermic injection, 

 which has largely replaced the above method, 

 the drug is injected by means of a syringe and 

 hollow needle into the loose connective tissue 

 beneath the skin. A graduated syringe holding 

 about 2 to 4 fluid drachms is used and the 

 injection made at a spot clear of the harness and 

 where the skin is freely movable, i.e. where sub- 

 cutaneous tissue is abundant. The side of the 

 neck, breast, behind the elbow, and flank are 

 convenient positions. 



By this method various alkaloids, sera, vac- 

 cines, mallein and tuberculin are administered. 

 Hypodermic solutions should be sterile and non- 

 irritant. The syringe and needle should be 

 thoroughly clean and sterilised by boiling or by 

 washing with 5 per cent, carbolic solution. This 

 precaution is doubly necessary when the syringe has been pre- 

 viously used for annuals suffering from contagious disease. 



The seat of operation should always be disinfected before injection. 

 Raising a fold of skin with the thumb and index finger of the left 

 hand the operator passes the needle along the fold or at right angles 

 to it into the subcutaneous tissue. When, as occasionally happens, 

 a blood-vessel is punctured, as shown by the escape of a few drops 

 of blood, the needle should be partly withdrawn, and if the bleeding 



Fig. 228.— Double- 

 acting syringe. 



