NEEDLES 



bottle filled with absolute alcohol [to which a few lumps of calcium chloride 

 may with advantage be added] or in a 3 per cent, solution of sodium borate. 



On account of the difficulty of preventing steel from rusting platinum-iridium 

 needles are gradually replacing steel. Platinum-iridium does not rust and 

 the needles can be heated to redness. On the other hand they are expensive 

 and delicate and as they are but little stronger than needles made of pure 

 platinum, it is on the whole better to use steel especially when a thick skin 

 has to be penetrated as is generally the case in animal inoculation. 



A selection of needles of different calibre and of different lengths ought to- 

 be kept in the laboratory. 



2. Preparation of the material for inoculation. 



The material to be inoculated may be either a solid or a liquid. The 

 procedure will be different in the two cases. 



(i) Of fluids. 



Broth cultures are the commonest fluids inoculated but other fluids, such 

 as blood, serum, pleural and peritoneal exudates, have also to be inoculated 

 at times. 



(a) Cultures. Every culture should be examined microscopically before being 

 inoculated, to test its purity. 



When ready to perform the inoculation remove a little of the culture with 

 a Pasteur pipette and transfer it to a sterile watch-glass and cover the latter 

 again with the paper in which it was sterilized. Aspirate the culture into a 

 sterile syringe through the needle either by puncturing the paper with the 

 needle or by slightly raising the paper and passing the needle beneath it. 

 Hold the syringe with the needle pointing upwards and gently press the 

 plunger to expel any air which may have been drawn into the syringe, taking 

 care to hold the piece of sterile paper which covered the watch-glass along- 

 side the needle to catch any drops of culture which may inadvertently be 

 driven out. Burn the paper and dip the watch-glass into a vessel of boiling 

 water to sterilize it. 



(b] Exudates. Blood and serous exudates must be collected in the manner 

 to be described in Chaps. XL and XII. With a pipette transfer the amount 

 required for inoculation to a sterile watch-glass and proceed as above. It 

 is very difficult to inject blood directly because it so readily coagulates and 

 blocks the needle. If the virus pass into the serum, the blood should be 

 allowed to clot and the serum used for inoculation. On the other hand if 

 the virus be retained in the clot this should be dealt with as though it were 

 a solid tissue (vide infra}. 



To facilitate the inoculation of whole blood it is occasionally necessary to have 

 resort to the anti-coagulating action of sodium citrate. The blood is collected in a 

 sterile vessel containing a little of the following solution also sterilized : 

 Water, - 1000 c.c. 



Sodium chloride, - 8 grams. 



Sodium citrate, - - 15 ,, 



Use two to four volumes of the citrate solution to one volume of blood. Mix 

 thoroughly and inoculate without delay. 



(ii) Of solid substances. 



(a) Solid substances. Fragments of internal organs, splinters, etc., maybe 

 inserted directly into the tissues of the animal. After making a small incision 

 separate the cellular tissue with a director and introduce the material into 

 the pocket so formed, suture the wound and cover it with collodion. Material 

 may be similarly introduced into the peritoneal cavity, muscles, etc. 



