646 ADMINISTEATION OF MEDICINES. 



Druggists issue medicines for hypodermic injection in exact doses 

 in hermetically closed tubes, and in tabloids of particular weights. 

 Guinard (" Encyclopedia V^terinaire ") gives the following 

 strength for hypodermic injections : — 



Aloin, 10 to 20 p.c. 



Cocaine, 2 to 5 p.c. 



Eserine, \ p.c. 



Salts of morphine and pilocarpine, 2 p.c. 



Strychnine, jV P-*^- 



THE OPERATION AND ITS SEAT.— These injections are made 

 by a syringe (Fig. 161, p. 647) which has a glass barrel and a 

 hollow needle. The most suitable substance for the manufacture 

 of the needle is an alloy of platinimi and iridium, which is hard, 

 rigid, and practically indestructible. It is well to have the piston 

 of asbestos, so that the syringe can be rendered free from'putre- 

 factive germs by immersing it for a few minutes in boiling water, 

 which in this case will not injure it. In order to prevent the 

 introduction of putrefactive or infective material under the skin 

 by this operation, we should, if possible, do it under antiseptic 

 precautions (p. 70), that is to say, disinfect the part, our hands, 

 and the syringe, and take care that the solution for injection is 

 free from contamination. For producing a general effect, it is 

 advisable to choose a spot where the skin is thin and loose, so that 

 the puncture may be easily made, and the injected fluid may have 

 plenty of room to become widely distributed. On this account, 

 these injections are generally made behind or in front of the lower 

 part of the shoulder, or on the breast. After the syringe has been 

 filled, it should be held with its point uppermost and the piston 

 slightly pressed, to permit the escape of the bubble of air which 

 might otherwise remain; because the entrance of air under the 

 skin might give rise to an abscess. A more or less horizontal fold 

 of skin, at the spot chosen, is taken up between the finger and 

 thumb of the left hand, and the point of the syringe, which is held 

 in the right hand, is passed perpendicularly through the base of 

 the fold, and is carried a little onwards, between the skin and the 

 flesh, which we should avoid hurting. The fluid is gradually 

 forced out by the pressure of the right thumb, and the syringe 

 slowly withdrawn. The first finger of the left hand is then placed 

 on the orifice, to prevent the fluid escaping, and the part which 

 contains the fluid is gently rubbed with the right hand, so as to 

 hasten absorption. It is sometimes more convenient to disconnect 

 the needle from the syringe, insert it, and then fix on the nozzle, 



